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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5201

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Introduction

Background and Previous Monitoring Studies

Severe water quality problems in Upper Klamath Lake have led to critical fishery concerns for the region, including the listing of Lost River and shortnose suckers as endangered in 1988 (Stubbs and White, 1993). The lake’s algal community has shifted to a near monoculture of Aphanizomenon flos-aquae (AFA) during summer (Kann, 1997; Perkins and others, 2000); massive blooms of the alga have been directly related to episodes of poor water quality in Upper Klamath Lake (fig. 1). The growth and decomposition of AFA blooms in the lake frequently cause extreme water quality conditions characterized by high pH (as much as 9–10), widely variable dissolved oxygen (anoxic to supersaturated), and high un-ionized ammonia concentrations (>0.5 mg/L). Large AFA blooms and their associated water quality concerns are also present in Agency Lake.

The U.S. Geological Survey (USGS), in cooperation with the Bureau of Reclamation, began monitoring water quality in Upper Klamath Lake in 2002. Before 2002, continuous data sets of temperature, pH, dissolved oxygen, or specific conductance of well-documented quality and spanning several months during the spring through autumn seasons did not exist. The Klamath Tribes have collected biweekly water samples for nutrients and chlorophyll a at 10 sites in Upper Klamath and Agency Lakes since 1990. Studies that have used this data set, which is the longest consistent record of the water quality in the Upper Klamath Lake, include Kann (2007) and Morace (2007).

From 2002 through 2004, the USGS continuous water quality monitoring program study area was limited to the northern part of Upper Klamath Lake, where the monitoring supported a telemetry tracking study of endangered adult suckers (Wood and others, 2006). The 3 years of monitoring showed that the occurrence and severity of poor water quality conditions in Upper Klamath Lake was unpredictable from year to year. However, in each year seasonal patterns of low dissolved oxygen and high pH were well described by the dynamics of annual AFA blooms (Hoilman and others, 2008). Seasonally low dissolved oxygen concentrations, for example, tend to occur near the end of July or beginning of August coincident with a collapse of the AFA bloom. A fish die-off in 2003 was associated with a particularly severe low dissolved oxygen event that coincided with a bloom decline at the end of July (Banish and others, 2009).

Circulation patterns in Upper Klamath Lake have been explored with measurements and modeling. Current velocity measurements made with acoustic Doppler current profilers (ADCPs; Gartner and others, 2007) and hydrodynamic modeling with the 3-dimensional UnTRIM model (Wood and others, 2008) have confirmed that during periods of prevailing northwesterly winds, circulation is clockwise around the lake, consisting of a broad and shallow southward flow through most of the lake and along the northern and eastern shorelines, and a narrow, deep, northward flow through the trench along the western shoreline. This description of the wind-driven currents indicates that poor water quality conditions, particularly low dissolved oxygen, that are observed in the northern part of the lake do not primarily originate locally. Instead, the circulation pattern could allow transportation of poor water quality conditions originating in the southern part of the lake through the trench west of Bare Island into the northern part of the lake.

In 2005, the USGS water quality monitoring program on Upper Klamath Lake expanded to include most of Upper Klamath Lake as well as sites in Agency Lake. Additional meteorological sites were established around the lake basin to provide greater resolution of meteorological data used in modeling water movement and heat transport in Upper Klamath Lake. Agency Lake was determined to have a seasonal cycle of AFA bloom and decline similar to, but independent from, that of Upper Klamath Lake. Dissolved oxygen production and consumption experiments in Upper Klamath Lake provided evidence that a decreasing trend of dissolved oxygen productivity through July could have contributed to decreasing dissolved oxygen levels observed in continuous monitor data during that time. Evidence of poor water quality conditions flowing northward through the trench along prevailing currents into the northern part of the lake also were observed (Hoilman and others, 2008).

Purpose and Scope

The long-term monitoring effort that began in 2005 was continued in 2006. This report presents the results of the 2006 data-collection program, which includes data from meteorological stations, laboratory analyses of water samples, dissolved oxygen production and consumption experiments, and continuous water quality monitors. To provide continuity, there are many similarities between the presentation of the 2006 data in this report and the presentation of the 2005 data in Hoilman and others (2008). This report also includes comparisons between 2005 and 2006, new analyses that use total nitrogen data, which was not collected in 2005, a more temporally complete data set of dissolved oxygen consumption and production experiments than was collected in 2005, and continuous water quality measurements from nearshore sites to compare to those from open-water sites.

Description of Study Area

Upper Klamath Lake (fig. 2) is in south-central Oregon. The lake is large and shallow with a surface area of 232 km² and an average depth of 2.8 m. Most of the lake (about 90 percent) is shallower than 4 m, except for a narrow trench running parallel to Eagle Ridge, on the lake’s western shore. This trench contains water as much as 15 m in depth. Upper Klamath Lake is in the Klamath Graben structural valley, and much of its 9,415-km² drainage basin is composed of volcanically derived soils. The largest single contributor of inflow to the lake is the Williamson River, which enters the lake near its northern end and on average contributes about 46 percent of the inflowing water.

Upper Klamath Lake is a natural water body, but lake-surface elevations have been regulated since 1921, when Link River Dam was completed at the southern outlet of the lake. The dam was built, and currently is operated, by the Bureau of Reclamation. The lake is now the primary water source for the Klamath Project, an irrigation system developed to supply water to farms and ranches in and around the Upper Klamath Basin (Bureau of Reclamation, 2000). Agency Lake, just north of Upper Klamath Lake is connected to Upper Klamath Lake by a narrow natural channel, and adds approximately 38 km² of surface area to the Upper Klamath Lake-Agency Lake hydrologic system (Johnson, 1985). Agency Lake is also shallow, with a maximum depth of approximately 3 m and an average depth of 0.9 m. Like Upper Klamath Lake, Agency Lake is hypereutrophic and has annual blooms of AFA. Because the channel connecting Upper Klamath Lake and Agency Lake is narrow compared to the two water bodies and the discharge through it is small, the two lakes are largely independent in terms of the seasonal AFA bloom and water quality dynamics.

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