The Clinton River drainage basin in southeastern Michigan was designated as an Area of Concern (AOC) in the 1980s by the International Joint Commission United States and Canada (1987). An AOC is a geographic area within the Great Lakes region that has been highly degraded by one or more of 14 beneficial use impairments (BUIs; International Joint Commission United States and Canada, 1987). These BUIs may be caused by contaminants from nonpoint urban and rural runoff or point sources including combined sewer overflows, municipal and industrial discharges, or contaminated sediments (Michigan Department of Natural Resources, 1988).

The Clinton River AOC encompasses the entire Clinton River drainage basin and nearshore areas of Lake St. Clair that are affected by discharge from the Clinton River mouth (fig. 1). Lake St. Clair Metropark Beach is roughly 3 miles west of the Clinton River mouth in Macomb County, Michigan, and is included in the Clinton River AOC because of high Escherichia coli (E. coli) concentrations in its recreational waters and frequent beach closures (U.S. Environmental Protection Agency, 2024). Beach closures are one of the 14 BUIs that categorize an AOC; therefore, because of its proximity to the Clinton River drainage basin, Lake St. Clair Metropark Beach is included in the Clinton River AOC. Beach managers make decisions on beach advisories and closures based on fecal indicator bacteria concentrations, including E. coli and enterococci, in their recreational waters of interest (U.S. Environmental Protection Agency, 2023). These closures and advisories are put in place to protect public health from disease-causing microorganisms (pathogenic bacteria, viruses, and protozoa) that are alongside E. coli in fecal waste and cause waterborne disease outbreaks (U.S. Environmental Protection Agency, 2012).

The U.S. Environmental Protection Agency has established recommendations for recreational water-quality criteria for the United States based on public health risk studies (U.S. Environmental Protection Agency, 2012). Based on these national criteria, the State of Michigan has established its own water-quality criteria for recreational waters (Michigan Department of Environmental Quality, 2006). Michigan’s guidelines state that “all waters of the state protected for total body contact recreation shall not contain more than 130 E. coli per 100 milliliters, as a 30-day geometric mean” (Michigan Department of Environmental Quality, 2006, p. 45). Furthermore, the guidelines state that waters designated for total body contact (TBC) recreation may not contain more than 300 E. coli per 100 milliliters (mL) for a geometric mean of at least three samples taken during the same sampling event in a defined sampling location (Michigan Department of Environmental Quality, 2006). The State of Michigan relies on county health departments to routinely test for E. coli at public swimming beaches to ensure that these criteria are not surpassed. In the event that E. coli concentrations exceed the water-quality criteria, the county health department will close the beach and continue monitoring until E. coli concentrations fall below the regulatory limits (Michigan Department of Environment, Great Lakes, and Energy, 2024c). Data collected from other entities, including the U.S. Geological Survey (USGS) for this and previous studies, are not considered when making regulatory decisions by county health departments on daily beach closures.

The Macomb County Health Department (MCHD) has monitored E. coli concentrations at Lake St. Clair Metropark Beach annually from April to September since 1995 and makes determinations for beach closures based on Michigan’s water-quality criteria (Macomb County Health Department, 2024). Results from water-quality monitoring from 2000 to 2005 were summarized by Fogarty (2007), who discovered that E. coli concentrations exceeded 1,000 colony-forming units (CFU)/100 mL (partial body contact standard; Michigan Department of Environment, Great Lakes, and Energy, 2024b) in 16 percent of all samples collected at Lake St. Clair Metropark Beach during that time. In the last 10 years (2013–23), the E. coli water-quality criteria have been frequently surpassed at Lake St. Clair Metropark Beach, resulting in 145 days of beach closures (Michigan Department of Environment, Great Lakes, and Energy, 2024a).

A hydrodynamic model to determine environmental explanatory variables for higher E. coli concentrations at Lake St. Clair Metropark Beach and another nearby beach on Lake St. Clair was completed in 2008 (Holtschlag and others, 2008). Results of that study indicated that rainfall before sampling events was positively associated with E. coli concentrations exceeding the TBC standard of 300 most probable number per 100 milliliters (MPN/100 mL) and that water temperature and turbidity were also important explanatory variables for E. coli concentrations at Lake St. Clair Metropark Beach. The Holtschlag and others (2008) study did not determine if the Clinton River was a source of E. coli to Lake St. Clair Metropark Beach, but it did find that increased streamflow from the Clinton River resulted in a decreased probability of high E. coli concentrations.

In an attempt to reduce the number of beach closures per recreational season, Huron-Clinton Metroparks first sought to identify the source of E. coli at Lake St. Clair Metropark Beach. In 2018, the USGS in cooperation with the Environmental Protection Agency and in collaboration with the Michigan Department of the Environment, Great Lakes, and Energy; MCHD; and Huron-Clinton Metroparks, began a study to monitor E. coli in Lake St. Clair Metropark Beach surface water, groundwater, and sediment; the Clinton River; and offshore areas of Lake St. Clair (Fogarty and others, 2021). That study also sought to determine the source of E. coli using microbial source tracking (MST) markers (Fogarty and others, 2021). Results of Fogarty and others (2021) indicated that the source of E. coli was likely local to the beach rather than coming from an outside source, such as the Clinton River or its drainage basin. Fogarty and others (2021) also found waterfowl, particularly the Larus species (gulls) and Branta canadensis (Canada geese), and to a lesser extent, human MST markers as potential sources of E. coli at Lake St. Clair Metropark Beach.

Given the results of Fogarty and others (2021), Huron-Clinton Metroparks implemented several beach restoration projects in an attempt to reduce E. coli at the beach and in the recreational waters at Lake St. Clair Metropark Beach. Beginning in 2021, Huron-Clinton Metroparks planted native grasses and plants upgradient from the sandy beach at Lake St. Clair Metropark Beach with the goal of discouraging waterfowl from landing in these areas. These vegetative buffers have been effective management strategies for geese in other areas because they block the geese’s line of sight for potential predators (Titchenell and Lynch, 2010). The native plants also serve to reduce stormwater runoff to the lake at Lake St. Clair Metropark Beach (Huron-Clinton Metroparks, 2024), which Fogarty and others (2021) identified as a potential transport mechanism of E. coli. Additionally, Huron-Clinton Metroparks installed acoustic bird deterrents along the edges of the beach, which replicate goose and gull distress sounds, to again discourage waterfowl from landing on the beach (Huron-Clinton Metroparks, 2024). Acoustic bird deterrents have been widely used in agricultural settings (Rivadeneira and others, 2018) and urban environments (Belant, 1997) and are commonly suggested as a means for reducing the number of nuisance gulls (Lowney and others, 2018). Although acoustic bird deterrents are a common solution to nuisance bird presence, waterfowl may become habituated to these sounds if other deterrent strategies are not implemented in tandem (Lowney and others, 2018; Rivadeneira and others, 2018). Finally, dogs trained for waterfowl harassment were hired to further deter birds from congregating at Lake St. Clair Metropark Beach. This strategy has been successful in several other Great Lakes beaches for the management of waterfowl to reduce bacterial levels and beach closures (Converse and others, 2012; Nevers and others, 2018; Jordan and others, 2019); however, the positive effects of this management strategy, when not paired with other bird deterrent strategies, have been a fairly short-term (weeks to months) solution (Hartmann and others, 2012; Nevers and others, 2018; Jordan and others, 2019). In this study, the USGS, in cooperation with the Michigan Department of the Environment, Great Lakes, and Energy and in collaboration with Huron-Clinton Metroparks and the MCHD, collected E. coli samples in surface water, groundwater, and sediment to determine if changes occurred after the restoration projects were completed.

Lake St. Clair Metropark Beach is a 938-acre public recreational area in Harrison Township, Macomb County, Mich. (fig. 1). Lake St. Clair Metropark Beach is surrounded by an urban area on the western shore of Lake St. Clair, just west of the mouth of the Clinton River, which has a 760-square-miledrainage basin that contains wetlands, forests, urban areas, agricultural areas, suburban areas, and parks (Fogarty and others, 2021). Lake St. Clair Metropark Beach includes ~600 feet (ft) of sandy beach, frequently used by recreators to access the Lake St. Clair Metropark Beach shallow swimming waters during summer months (May through September). The MCHD has been collecting surface-water E. coli samples two times per week during the recreation season and in at least three locations in the swimming beach per sampling date since 1995, and their data are used to make determinations on beach closures (Macomb County Health Department, 2024).

The USGS collected E. coli samples from May through September 2022 and 2023 in shallow nearshore surface water (number of samples [n]=480), shallow groundwater (n=72), and beach sediment (n=144) near the recreational waters at Lake St. Clair Metropark Beach (fig. 1; table 1). Six nearshore surface-water locations were sampled twice per week over 20 weeks from May to September in 2022 and 2023 (fig. 1). USGS and MCHD did not collect surface-water samples on the same days. Surface-water sampling locations were spread across the entire recreational swimming area, approximately 120 ft apart. Groundwater samples were collected from 6 sampling sites on the beach—3 close to the lake interphase, where the lake meets the land, (site short name ending in “A” on table 1) and 3 ~100 ft from the lake interphase (site short name ending in “C” on table 1)—6 times during each of the 2022 and 2023 sampling seasons (fig. 1). At the same time groundwater samples were collected, sediment samples were collected from the surface of the recreational beach and from the same depth that groundwater samples were taken (average depth of ~2 ft). Samples were collected during various wet (more than 0.10 inches of rain within 24 hours prior to sampling) and dry (less than 0.10 inches of rain within 24 hours prior to sampling) weather conditions. Groundwater seepage measurements were taken five times in 2022 (June, July, and August) and twice in 2023 (August), again during various wet and dry weather conditions. These measurements were taken in the shallow, nearshore waters of Lake St. Clair in at least two locations per measurement event. Volunteers and staff at Lake St. Clair Metropark Beach monitored the number and location of gulls and Canada geese on the beach near the recreational waters and in five other zones of the Metropark in 2021, 2022, and 2023. Volunteers enumerated birds at least 2 days a week during recreational seasons, but often up to 6 days per week, and occasionally several times per day, depending on volunteer availability (Byers, 2026). The duration of each observation was also variable and depended upon location, bird movements, and weather patterns.

All results from E. coli sampling are available in the USGS National Water Information System database (U.S. Geological Survey, 2025), which is accessible through the Water Quality Portal (National Water Quality Monitoring Council, 2024) by using the USGS station numbers in table 1. Groundwater seepage measurements and waterfowl enumeration data are presented in Byers (2026). Meteorological data from the National Oceanic and Atmospheric Administration Mount Clemens Air National Guard Base (USW00014804; National Oceanic and Atmospheric Administration, 2024) were used for all meteorological comparisons.

Quality assurance and quality control samples were collected for all sample types to verify precision of analytical methods and identify any contamination in field samples. A total of 45 sequential replicate E. coli samples (~9 percent of surface-water samples analyzed) were collected from surface water, and 17 field blanks of sterile deionized water (~4 percent of the surface-water samples analyzed) for surface-water methods were collected. In addition, 6 sequential replicates (~8 percent of the groundwater samples analyzed) were collected from groundwater, and 12 field blanks of sterile deionized water (~17 percent of the groundwater samples analyzed) were also taken for groundwater methods. Finally, 12 sequential replicates (~8 percent of the sediment samples analyzed) were taken from sediment samples at the surface of the beach and at the same depth as groundwater samples. A laboratory blank sample for E. coli was analyzed by MI-BaRL for each sampling day (40 sampling days per recreational season).

Escherichia coli was not detected in any field blank sample taken with surface-water or groundwater methods or in any laboratory blank sample; therefore, little to no bias from outside contamination is expected to affect sample results. Replicate surface-water sample pairs had an average relative percentage difference (the difference between the two values, divided by the average of the two values, multiplied by 100) of 42 percent. Groundwater samples had a 30-percent average relative percentage difference, and sediment samples had 64- percent and 29-percent average relative percentage difference in surface and deep samples, respectively. This variability in E. coli concentrations is typical of field studies (for example, Fogarty and others, 2021) because E. coli is highly variable in the environment. Replicate samples tended to be of the same order of magnitude as their environmental sample counterparts and fell within the same relative percentage difference ranges observed by Fogarty and others (2021).

Groundwater seepage rates were highly variable throughout the 2022–23 recreational seasons (table 3; Byers, 2026). The positive and negative values of the seepage rates shown in table 3 indicate the direction of groundwater flow. Positive seepage rates indicate that the shallow groundwater at Lake St. Clair Metropark Beach was generally flowing toward the recreational waters at the time seepage measurements were made, and negative seepage rates indicate that the recreational waters were losing to the shallow groundwater on that sampling date. Groundwater seepage rates in August of 2022 and 2023 had daily average values ranging from −0.81 to 1.23 centimeters per day (cm/d; table 3). The maximum and minimum groundwater seepage values for August of both years were in 2023. Positive average seepage values were measured on three of the five August sampling dates, and negative average values were measured on the other two days. In June and July of 2022, daily average seepage measurements yielded much higher or lower values than those observed in August, ranging from −23.4 cm/d in July to 7.94 cm/d in June. All seepage rate values from 2022 and 2023 fall within the expected range of previously observed values in coastal freshwater environments, from (positive or negative) 0.01 cm/d (Lee and Cherry, 1979) to greater than (positive or negative) 100 cm/d (Asbury, 1990; Rosenberry, 2000).

The faster seepage rates in June and July of 2022 indicate a temporal variability in seepage rates at Lake St. Clair Metropark Beach. Previous research in lacustrine environments revealed that temporal variation in groundwater seepage rates may have several causes, including lake seiche events (Taniguchi and Fukuo, 1996), which have been demonstrated locally to propagate through and be dissipated by Lake St. Clair from the St. Clair and Detroit Rivers (not shown on fig. 1; Jackson, 2016). Additional potential causes of variation in groundwater flow rates include diurnal effects of evapotranspiration (Rosenberry and others, 2013), precipitation events (Rosenberry and Morin, 2004; Rosenberry and others, 2013), and tidal effects (Rosenberry and others, 2013), which all may affect the relative positions of the groundwater potentiometric surface and lake level. Further measurements of groundwater seepage throughout the recreational season could help to better characterize the dominant direction and magnitude of groundwater seepage at Lake St. Clair Metropark Beach and to better understand the ways in which groundwater and surface water interact at the lake interphase.

Waterfowl, particularly gulls and geese, are a likely source of E. coli at Lake St. Clair Metropark Beach (Fogarty and others, 2021). Restoration efforts at Lake St. Clair Metropark Beach were mainly focused on reducing the number of waterfowl that congregated on the beach in hopes that reducing this source would reduce E. coli concentrations. In 2021, beach managers at Lake St. Clair Metropark Beach planted native grasses as a vegetative buffer and installed acoustic bird deterrents as potential long-term solutions to deter nuisance waterfowl. Dogs trained in waterfowl harassment were implemented as a short-term solution to deter birds in the summer recreation season of 2021.

Overall, gulls were much more common than geese at Lake St. Clair Metropark Beach and numbers generally declined between 2021 and 2023 (table 4). Gulls made up 89, 90, and 94 percent of the total number of birds enumerated in all of Lake St. Clair Metropark Beach in 2021, 2022, and 2023, respectively, with geese making up the remaining percentages. Of all the gulls enumerated, 81, 60, and 69 percent were on the recreational beach in 2021, 2022, and 2023, respectively. The average number of gulls counted per day on the recreational beach decreased from 131 gulls per day in 2021 to 62 gulls per day in 2022 and 83 gulls per day in 2023 (table 4). Far fewer geese than gulls were enumerated throughout the park and, specifically, on the recreational beach. On average, one goose per day was counted on the recreational beach in 2021 and 2022, and no geese were counted, on average, in 2023. The total number of geese enumerated on the recreational beach decreased from 120 to 30 geese from 2021 to 2023 (table 4). In the rest of the park at Lake St. Clair Metropark Beach, geese were observed more frequently but still with decreasing trends from 1,578 geese in 2021 to 660 geese in 2023 (table 4). Additionally, a reduction in the average number of birds (gulls plus geese) that were counted in all of Lake St. Clair Metropark Beach each day was observed, from 181 birds per day in 2021 to 114 birds per day in 2022 and 127 birds per day in 2023 (table 4).

Escherichia coli concentrations from the recreational (surface) water, groundwater, and sediment samples collected during this study for the 2022 and 2023 recreational seasons were compared to those collected by Fogarty and others (2021) in 2018 and 2019. Between the study by Fogarty and others (2021) and this study, beach restoration projects were implemented to discourage waterfowl from congregating on the beach at Lake St. Clair Metropark Beach. Escherichia coli concentrations from before and after beach restoration projects were compared to determine if consistent changes in E. coli concentrations were observed in surface water, groundwater, or sediment. Weather conditions were variable throughout both sampling periods, but both studies captured similar precipitation and temperature conditions throughout the recreational seasons (table 5; National Oceanic and Atmospheric Administration, 2024). At Lake St. Clair Metropark Beach, July tended to be the warmest and driest month in all years analyzed. May, June, and August tended to be wetter than July and September (table 5). The greatest amount of precipitation was recorded in 2023, which was also the coolest recreational season sampled. The warmest year of the study period was 2018 (table 5).

An overall decrease in surface-water E. coli concentrations was observed when comparing pre- and postrestoration samples in both USGS- and MCHD-collected data; however, increased variability was observed in MCHD data after restoration (fig. 4). The number of beach closures increased following restoration efforts, indicating that more high E. coli concentration events occurred postrestoration, and the conditions that caused these events persisted. Other studies have documented reductions in E. coli concentrations in surface water following waterfowl harassment with dogs (Converse and others, 2012; Nevers and others, 2018; Jordan and others, 2019); however, these studies measured E. coli immediately following this treatment strategy. Measurements for our study were made at least one year after waterfowl harassment dogs were employed at Lake St. Clair Metropark Beach; therefore, reductions cannot be directly attributed to bird harassment as they have been in previous studies. Acoustic bird deterrents have also been proven effective in reducing gull presence near freshwater sources, thereby reducing E. coli concentrations in surface water (Benton and others, 1983). Benton and others (1983) found that the reduction in gulls and associated reduction in E. coli lasted at least 14 months after the initial installation of bird deterrent systems, at which time they concluded their study. This prolonged reduction in E. coli in surface water after the use of acoustic bird deterrents demonstrates that the ongoing measures put in place by Lake St. Clair Metropark Beach to reduce waterfowl presence may be affecting surface-water E. coli concentrations, but those effects are not substantial enough to reduce beach closures within two years of implementation.

A significant reduction of E. coli in sediment samples was observed after the restoration efforts at Lake St. Clair Metropark Beach. Although E. coli in beach sediment is not monitored for regulatory reasons, this reduction in surface-sediment E. coli concentrations may have larger implications for the overall reduction of E. coli at Lake St. Clair Metropark Beach. Few other studies have evaluated the presence of E. coli in beach sands before and after restoration actions similar to those performed at Lake St. Clair Metropark Beach; that is, use of canid harassment, acoustic bird deterrents, and (or) vegetated buffer zones. Other studies have demonstrated that different types of restoration actions, specifically those that replace beach sand containing high E. coli concentrations with E. coli-free sand (Whitman and Nevers, 2003) or add exogenous sand on top of sand that previously had fecal indicator bacteria issues (Hernandez and others, 2014), were effective in reducing E. coli and other fecal indicator bacteria in beach sands.

At Lake St. Clair Metropark Beach, sediment samples on the surface of the beach tended to have higher E. coli concentrations than those at depth. Similarly, Whitman and Nevers (2003) found higher E. coli concentrations in sediment samples taken at shallower depths compared to samples taken beneath the water table at a Lake Michigan beach. The findings of this study, along with those of Whitman and Nevers (2003), indicate that average E. coli concentrations in sediment at or below the water table are generally an order of magnitude lower than those at the surface (table 2). High E. coli concentrations at the surface of the beach have locally been attributed to waterfowl or human sources through MST (Fogarty and others, 2021), which are consistent with observations amongst other Great Lakes beaches (Standridge and others, 1979; Whitman and Nevers, 2003; Ishii and others, 2007; Halliday and Gast, 2010; Nevers and others, 2022).

Since the restoration projects were implemented at Lake St. Clair Metropark Beach in 2021, the total number of birds on the recreational beach have generally decreased (table 4). Decreased waterfowl numbers may be a factor in reducing E. coli concentrations in sediment at Lake St. Clair Metropark Beach, but this study was not designed to demonstrate a causal relationship between bird numbers and E. coli. Previous studies have concluded that restoration actions similar to those taken at Lake St. Clair Metropark Beach can decrease the number of gulls and geese on recreational beaches (Benton and others, 1983; Titchenell and Lynch, 2010; Converse and others, 2012; Nevers and others, 2018). Enumeration of waterfowl at Lake St. Clair Metropark Beach only offers a snapshot of bird presence on the recreational beach, and the actual number of birds congregating on the beach may be over- or underestimated by these daily counts over the course of the recreational seasons.

Escherichia coli concentrations in sediment and groundwater samples tended to be higher close to the lake interphase compared to samples taken ~100 ft from the lake interphase (figs. 3B–D). Previous research has revealed that groundwater beneath wet sand, close to a lake interphase, is more likely to have elevated E. coli concentrations than locations beneath dry sand (Crowe and Milne, 2013). Similarly, nearshore beach sediment has been identified as a reservoir for E. coli in several Great Lakes beaches (Kinzelman and others, 2003; Beversdorf and others, 2007; Ishii and others, 2007; Whitman and others, 2014; Wu and others, 2017). Fogarty and others (2021) posited that there may be a reservoir of E. coli in beach sediment at Lake St. Clair Metropark Beach, wherein E. coli colonies can establish populations and grow in quantity throughout the recreational season. Bacteria have been observed to survive longer in sediment than in water because of higher available organic matter content, which is required for growth, and protection from ultraviolet radiation (Francy and Darner, 1998; Alm and others, 2006; Rumball and others, 2021).

One important factor that likely contributes to the higher E. coli concentrations in groundwater and sediment near the lake interphase is shoreline erosion caused by wave action. As waves crash against shoreline sediment, E. coli bound to sand grains may become resuspended in the water column (Vogel and others, 2016; Safaie and others, 2021; Nevers and others, 2022). This mechanical separation of E. coli and other fecal indicator bacteria from nearshore sand grains allows the bacteria to then be transported and recirculated through nearshore surface water and shallow groundwater (Vogel and others, 2016; Wu and others, 2017). Transport of fecal indicator bacteria, including E. coli, from nearshore sediment has been observed to increase E. coli concentrations in nearshore surface waters to levels that may exceed water-quality criteria and lead to public health advisories (Wu and others, 2017; Palmer and others, 2020). At Lake St. Clair Metropark Beach, resuspension and transport of bacteria may be of concern in terms of beach closures, as E. coli concentrations in groundwater (fig. 3B) and near the lake interphase in surface (fig. 3C) and deep sediment (fig. 3D) tended to be at least an order of magnitude higher than the associated surface-water value (fig. 3A).

Other factors that may provide transport mechanisms for E. coli at Lake St. Clair Metropark Beach include precipitation, which may transport E. coli through sediment via infiltration, potentially adding to the E. coli reservoir (Beversdorf and others, 2007; Ishii and others, 2007; Malott and others, 2016; Fogarty and others, 2021), and groundwater seepage (Whitman and others, 2001). Groundwater seepage measurements at Lake St. Clair Metropark Beach revealed some positive values, indicating that groundwater discharged to recreational waters during both recreational seasons (table 3). Whitman and others (2001) found that E. coli concentrations within seepage fluxes at another Great Lakes beach tended to be highly variable; concentrations ranged from <100 to >50,000 MPN/100 mL. A later study at that same beach concluded that groundwater seepage did not contribute a substantial amount of E. coli to the receiving surface waters (Whitman and Nevers, 2003). When groundwater was discharging into the recreational waters at Lake St. Clair Metropark Beach, it is possible that E. coli was being transported to surface water, although direct measurements of E. coli in the seepage waters would be needed to understand how E. coli are transported locally. Negative groundwater seepage rates were also measured at Lake St. Clair Metropark Beach (table 3), indicating that the recreational waters were flowing into groundwater occasionally throughout the study period. This indicates that E. coli may occasionally be transported from surface water to the shallow groundwater at Lake St. Clair Metropark Beach, depending on the conditions of groundwater and surface-water interactions. More measurements of groundwater seepage over time could help to determine the prevailing direction of groundwater flow and the effect that fluxes of E. coli have on surface-water and groundwater bacterial concentrations.

Previous work at Lake St. Clair Metropark Beach by Holtschlag and others (2008) and Fogarty and others (2021) had conflicting findings on the correlation between precipitation and the concentration of E. coli in surface water. Holtschlag and others (2008) found that rainfall before E. coli sampling was positively correlated with E. coli concentrations, whereas Fogarty and others (2021) found no correlation between the two factors. Correlations between environmental factors and E. coli were not analyzed as part of this study, so uncertainty about the effects of factors such as precipitation remain. A consistent relationship did not exist between the distribution of E. coli concentrations in each recreational season and the recreational season average maximum temperature, average minimum temperature, or precipitation total. For example, in 2023, groundwater, surface sediment, and deep sediment, on average, had the lowest concentrations of E. coli measured for all years during this study (figs. 3B–D). That same year, precipitation totals were highest amongst the study years, and temperatures were generally the lowest (table 5). Other studies have concluded that increased precipitation often leads to increased concentrations of E. coli (Haack and others, 2003; Beversdorf and others, 2007); this was not the case at Lake St. Clair Metropark Beach in 2023, potentially because of the cooler temperatures. Conversely, in 2019, which had the second-highest season-long precipitation total, E. coli concentrations were substantially higher than in 2023, particularly in surface sediment, potentially indicating agreement with the previous studies. Also, 2019 had the highest maximum air temperature (table 5), which may promote E. coli growth; however, all seasonal maximum temperatures observed fell within the range for optimal E. coli growth (73–90 degrees Fahrenheit; Beversdorf and others, 2007; Ishii and others, 2007; Weiskerger and others, 2019). The recreational season with the least precipitation, 2022, had the lowest maximum E. coli concentration in surface water, which again seems to agree with previous works on the effects of precipitation to E. coli concentrations. Seasonal averages and totals do not provide a refined or detailed look at relations between E. coli and environmental factors like temperature and precipitation. A more detailed analysis would help to disentangle the confounding effects of environmental conditions and beach restoration efforts.

The objective of this study was to evaluate Escherichia coli (E. coli) concentrations in surface water, groundwater, and sediment at Lake St. Clair Metropark Beach in Macomb County, Michigan, before and after implementation of restoration projects intended to reduce beach closures caused by high E. coli concentrations. Lake St. Clair Metropark Beach has a history of beach closures because of elevated E. coli concentrations that exceed the State of Michigan’s total body contact recreation standards of 300 most probable number (of bacteria) per 100 milliliters (MPN/100 mL) as a geometric mean of at least three samples taken the same day and (or) 130 MPN/100 mL as a 30-day geometric mean. These elevated E. coli concentrations and associated beach closures have caused Lake St. Clair Metropark Beach to be included in the Clinton River Area of Concern under the beach closure beneficial use impairment. Huron-Clinton Metroparks implemented several beach restoration projects in 2021 after a study concluded that waterfowl or humans local to the beach may be sources of E. coli. These restoration projects sought to reduce E. coli concentrations at Lake St. Clair Metropark Beach by reducing the number of waterfowl that congregate in the recreational areas. After these restoration projects, this 2-year study, completed in cooperation with the Michigan Department of the Environment, Great Lakes, and Energy and in collaboration with Huron-Clinton Metroparks and the Macomb County Health Department, found variable surface-water E. coli concentrations, and groundwater and sediment E. coli concentrations that were orders of magnitude higher than those of surface water. Data from this study were compared to prerestoration data from 2018-19 published in Fogarty and others (2021). These comparisons revealed that surface-water and sediment E. coli concentrations were significantly lower after beach restoration. The apparent decrease in surface-water concentrations may be due, in part, to the shorter sampling seasons in 2018 and 2019. During 2018 and 2019, the warmest parts of the recreational season were over-represented resulting in a concentration distribution that may have been biased high. Surface-water data collected by the Macomb County Health Department represented the full recreational season (May through September) in all years. The distribution of Macomb County Health Department data also generally decreased from before restoration to after restoration, although the data are more variable after restoration. Although E. coli concentrations in surface water were typically lower after restoration, more beach closures attributed to high E. coli concentration events were observed based on Macomb County Health Department data. The conditions that produced these high E. coli concentrations in surface water persisted at Lake St. Clair Metropark Beach for at least two years postrestoration. There was a significant decrease in surface-sediment E. coli concentrations following restoration and a general decrease in waterfowl numbers between 2021 and 2023, which may indicate that the bird deterrence measures could be influencing E. coli concentrations in sediment and surface water, although a causal relationship cannot be concluded. Groundwater E. coli concentrations before and after restoration were variable and did not appear to be correlated with the timing of restoration efforts. Groundwater E. coli concentrations were not significantly different before and after restoration, but sediment and groundwater E. coli concentrations were an order of magnitude lower in 2023 compared to previous years of analyzed data. Groundwater seepage rates reveal that groundwater discharges to surface water at times, which indicates that groundwater could be transporting E. coli to the recreational waters. Overall, there are mixed results on the relation between E. coli concentration decreases and restoration efforts. The greater number of beach closures postrestoration indicates that conditions leading to high E. coli concentrations at Lake St. Clair Metropark Beach persist. Continued monitoring of E. coli at Lake St. Clair Metropark Beach could help to determine whether the decreasing E. coli trends observed in U.S. Geological Survey and Macomb County Health Department data continue. Future work could explicitly consider effects of environmental factors, further characterize the role of surface-water and groundwater interactions affecting the surface-water quality, and (or) determine the role of the potential E. coli reservoir in the beach sediment on water quality.