Fact Sheet 077–02

August 2002

Revised May 2005

Monitoring Our Rivers and Streams

By Martha L. Erwin and Pixie A. Hamilton

The PDF for the report is 779 kb

All of life depends on water, and all of us are citizens of a watershed. Our activities and the ways we use our water resources and the land adjacent to the water affect the quality of our drinking water, our recreational opportunities, and the health and diversity of aquatic plants and animals. Our activities also affect whether our rivers and streams will continue to be beautiful places to visit and vistas to contemplate.

In this publication, you'll find information about watersheds and about monitoring the quality and quantity of surface-water resources. You'll learn how the U.S. Geological Survey (USGS) monitors streamflow and surface-water quality across the Nation and how USGS information can help you learn more about your water resources—whether as a citizen of your watershed or an active citizen monitor.

This publication focuses on surface water, but keep in mind that surface water and ground water are interconnected. USGS also monitors the flow and quality of ground water, and investigates surface- and ground-water interactions.


Stream-gaging station on the American River near Nile, WA (USGS Station No. 12488500), one of more than 6,600 across the Nation with real-time streamflow data. (Photo by Van Wilson, USGS.)

USGS and citizen monitoring

The water quality of a nearby stream, a watershed, or a large river system can be enhanced only by collecting good information about conditions and by responding—most effectively at the local level—to that information. Informed citizens of a watershed often are in the best position to identify priority water issues and to understand the political, social, and economic context in which those issues are addressed. USGS works with citizen monitors in many watersheds across the Nation. Typically, watershed associations, such as the Alliance for Chesapeake Bay and Watershed Committee of the Ozarks, plan and conduct the activities of citizen monitors. Citizen monitoring enhances the monitoring conducted by USGS and other federal and state agencies by filling in geographic gaps or by increasing the frequency of sampling. Information collected by citizen monitors can also help USGS and other water-resource agencies know where to focus their broader data-collection activities and analysis. In turn, hydrologists from USGS and other agencies often train citizens during "side-by-side" data-collection activities.


A citizen monitor with Alliance for Chesapeake Bay prepares to collect water samples near the U.S. Naval Academy, where submerged aquatic vegetation is being replanted. Some citizen data were used in USGS studies of these aquatic plants, which are vital to the Bay's health. (Photo by Bob Murphy, Alliance for Chesapeake Bay.)

To learn about USGS monitoring activities in your state, call or e-mail the USGS representative. A list of contacts is at

Understanding your watershed

Natural features, such as topography, define watersheds—land areas that receive rain or snow and drain to specific surface-water bodies, such as streams, rivers, lakes, reservoirs, bays, or oceans. Both natural and human-induced conditions within the watershed are reflected in the quality of the surface water.

More and more, water-quality management and policies are being developed in terms of the watershed, rather than being couched in terms of cultural boundaries, such as counties and states. While many federal and state agencies focus on the larger river systems and associated watersheds, local agencies and citizens usually are concerned with the smaller watersheds where they live. Because the smaller watersheds are "nested" within the larger river networks, and because many watersheds cross jurisdictions, successful watershed management requires that everyone work together—citizens and water-resource professionals, and local, state, interstate, and national stakeholders.

A standardized watershed classification system—the Hydrologic Unit System—was developed in the mid-1970s by USGS under the sponsorship of the U.S. Water Resources Council. The goal was to delineate and map hydrologic boundaries and enable a variety of organizations and programs to share information and coordinate management of watersheds.

Hydrologic units are a topographically defined set of watershed boundaries, organized in a nested hierarchy by size. The system divides the Nation into 21 regions (representing some of our largest rivers, such as the Missouri, Susquehanna, and Columbia Rivers), and progressively smaller sub-regions, accounting units, and cataloging units. Each cataloging unit is assigned an 8-digit code (its hydrologic unit code, or HUC) having two digits for each of the four levels.

The 8-digit HUCs are used widely, such as in the U.S. Environmental Protection Agency (EPA) Water Information Network (described below). The geographical area of the cataloging units is often too large, however, for management at the local level, such as for land-use planning. Therefore, USGS, U.S. Department of Agriculture, EPA, and other federal agencies and interested states are in the process of subdividing cataloging units into watersheds (average size 40,000–250,000 acres) and sub-watersheds (10,000–40,000 acres). For information on HUC maps and watersheds in your State, call 1-888-ASK-USGS or go to


To locate and learn about your watershed, go to EPA's Water Information Network at and click on "Surf Your Watershed," then on "Locate Your Watershed."

Search by map, stream name, zip code, county, Tribal nation, or other geographic names to find your watershed and its hydrologic unit code (HUC). For example, if you live in Tennessee and your zip code is 37919, you live in the Watts Bar Lake Watershed, which is HUC 06010201.

A monitoring protocol

Monitoring is necessary to ensure that our waters can continue to support the many different ways we use these resources and to track whether protection and restoration measures are working. The information gained from monitoring helps with prioritizing the issues to be addressed and choosing the geographic areas in which to concentrate, thus helping to ensure cost-effective water-resource management.

Effective monitoring is regular, long term, and includes biological, physical, and chemical measurements.

A "hydrologic context" for your monitoring data

Information from USGS monitoring can help you understand more about the significance of the conditions you observe or measure in your watershed. Several characteristics of USGS monitoring provide this "hydrologic context":

Monitoring is at different scales and in different environmental settings

USGS investigates local issues and trends in a particular stream or in a particular county, as well as larger regional systems, such as the Mississippi River Basin. Methods of sampling and analysis are uniform, and monitoring is done at sites that are representative of watersheds across the Nation, so that comprehensive assessments can be made at larger, even national, scales. This multi-scale approach helps to determine if certain types of water-quality issues are isolated or pervasive, and allows streams and rivers to be compared to those in other geographic and environmental settings. Therefore, the data can help answer questions like—

Monitoring is regular and long term

USGS has been collecting data for more than a century at some of its monitoring stations. Long-term data collection creates a set of baseline data that can be used to assess the significance of observed changes. For example, collecting data on our water resources over the long term helps answer questions like—

Nationwide streamflow data are available on the Web


This map highlights areas experiencing dry conditions over the past 7 days, from below-normal streamflows (lightest colored dots) to "extreme hydrologic drought" (red dots). "Normal" streamflow is defined in the context of conditions that have been recorded at a streamflow-gaging station at the same time of year over the past 30 or more years. Maps like this one, and other maps and graphs of streamflow conditions are available on the USGS WaterWatch Web site at


Current meter


Technicians are measuring discharge, the volume of water passing a given stream cross section in a given period of time (reported as cubic feet per second, or ft3/s). Another type of data collected to determine streamflow is stage (or "gage height"), the height of the water above an arbitrary reference point set at the gaging station. Stage measurements are continuously recorded by equipment inside a gagehouse located on the stream bank and relayed via telephones or satellites to USGS offices. It isn't practical for people to make continuous discharge measurements, so daily discharge values (provisional "real-time" values reported on the Web) are computed on the basis of a mathematical relation between the river's stage and discharge. (Photo by Michael Coakley, USGS.)

Currently, USGS regularly collects streamflow data at more than 7,200 sites ("gaging stations"). Most of the stations are funded and operated in cooperation with other federal agencies, such as the U.S. Army Corps of Engineers, and with state, Tribal, county, and municipal agencies, who use these data for making decisions such as when to withdraw water from rivers or reservoirs and whether to permit discharge of treated wastewater. Provisional data from more than 6,600 of these stations are available in "real time" (updated at intervals of 4 hours or less) at

Access to streamflow data allows for more accurate interpretation of water-quality data. An observed trend in water quality—for example, increasing concentrations of a contaminant in a stream over a six-month period—may indicate an actual water-quality change or may be the indirect result of differences in the distribution of flow volumes when the water samples were collected.

Nationwide water-quality data are available on the Web

USGS collects samples from streams across the Nation and analyzes for chemical, physical, and biological properties of water, sediment, and tissue. Data are collected for investigations that range from national in scale, such as the National Water-Quality Assessment Program (NAWQA), to studies in small watersheds. Typical field measurements (made directly in the stream or on the streambank) include pH, water temperature, dissolved oxygen, and turbidity.

Other field measurements include specific conductance (conductivity), an indirect indicator of dissolved minerals, acids, and metals in the water; and alkalinity, an indicator of water's ability to neutralize acids and keep the pH constant. Currently, selected field measurements are available in real-time from more than 1,100 USGS sites at

Other chemical measurements—such as analyses for concentrations of major ions, nutrients, trace elements, pesticides, volatile organic compounds, radioactive chemicals, and organic wastewater contaminants—are made in the laboratory. The USGS National Water-Quality Laboratory in Denver, Colo., specializes in environmental analytical chemistry, and features standardized laboratory methods and quality-assurance and quality-control protocols. In addition, the laboratory methods can detect concentrations at very low levels—commonly 10 to 1,000 times lower than the EPA standards and guidelines. These sensitive methods allow for an early detection of potentially harmful contaminants before they reach levels of concern, and allow for trends to be detected for constituents that are difficult to measure.


Biologists with the USGS National Water-Quality Assessment (NAWQA) Program are collecting benthic (bottom-dwelling) invertebrates for analysis. USGS also monitors for concentrations of total coliform bacteria and viruses; fish-tissue contaminants (such as mercury, DDT, and dioxin); and algae. (Photo by Denis Sun, USGS.)

USGS monitoring is for assessment only

USGS has no regulatory responsibilities and focuses on evaluating the entire resource, which may be a source of drinking water as well as of water used for industry, irrigation, and recreation. USGS water-quality data thereby complement much of the data collected by the States and by EPA, which focus on monitoring for compliance with regulations.



Graphs of real-time discharge values can help you decide if it's a good time for an outing on the river. Discharge data also help with interpretation of water-quality data. For example, an increase in turbidity values (top graph) corresponded with increasing streamflow (bottom graph) at the James River at Cartersville, VA, gaging station in September 2004. This station is one of more than 1,100 across the Nation with real-time data on both water quality and water quantity.

Visit for access to online maps, data, and reports, including:

For printed reports and maps

Call 1-888-ASK-USGS
Or, write to:
USGS, Information Services
Box 25286, Denver Federal Center
Denver, CO 80225
Or, fax requests to (303) 202-4693

Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 6.0, which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.

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