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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5026

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Introduction

Water quality degradation in Upper Klamath Lake has led to critical fishery concerns for the region, including the listing of Lost River and shortnose suckers as endangered in 1988. The algal community of the lake has shifted to a near monoculture of the cyanobacterium (blue-green algae) Aphanizomenon flos‑aquae (AFA) during summer (Kann, 1997; Perkins and others, 2000), massive blooms of which 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 values (9–10), widely variable dissolved oxygen conditions (anoxic to supersaturated), and high un-ionized ammonia concentrations (greater than 0.5 mg/L). Large blooms of AFA and the associated water quality concerns also occur in Agency Lake.

Before the U.S. Geological Survey (USGS) began monitoring water quality in Upper Klamath Lake in 2002 in cooperation with the Bureau of Reclamation, continuous datasets of temperature, pH, dissolved oxygen, or specific conductance spanning spring through fall 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. Several studies have used this dataset, which is the longest consistent record of water quality available for Upper Klamath Lake (Wood and others, 1996; Kann and Smith, 1999; Kann and Walker, 2001; Kann and Welch, 2005; Wood and others, 2006; Morace, 2007).

During 2002–04, the USGS water quality monitoring program study area was limited mostly to the northern one-third of Upper Klamath Lake, where the monitoring supported a telemetry tracking study of endangered adult suckers (Wood and others, 2006). Data collected during the 3 years of monitoring showed that the occurrence and severity of poor water quality conditions in Upper Klamath Lake were unpredictable from year to year. During each year, however, seasonal patterns of low dissolved oxygen concentration and high pH coincided with blooms of AFA that occur in the lake. A diel pattern of water column stratification was observed in the lake, but the data did not indicate a strong association between water column stratification and an event of extreme low dissolved oxygen concentration and a consequent fish die-off in 2003.

Water circulation in Upper Klamath Lake is determined by wind speed and direction and the bathymetry of the lake. The lake is mostly shallow (less than 3.5-m depth), with the exception of a narrow trench (greater than 10-m depth) that extends along the western shoreline (fig. 2). Prevailing winds over Upper Klamath Lake are westerly (between about 250 and 315 degrees) over the northern part of the lake and then are constrained by the surrounding topography to northwesterly (between about 315 and 360 degrees) over the southern part of the lake. Velocity measurements of currents made with acoustic Doppler current profilers (ADCPs, Wood and others, 2006) and hydrodynamic modeling with the three-dimensional UnTRIM model (Cheng and others, 2005) have confirmed that circulation is clockwise around the lake during periods of prevailing winds, consisting of a broad and shallow southward flow through most of the lake and a narrow, deep, northward flow through the trench along the western shoreline. The direction of the current in the trench is tightly constrained by the bathymetry to flow to the northwest at about 320 degrees when forced by prevailing winds. Some of the water exiting the trench just west of Bare Island continues clockwise around the island, and the rest turns west around Eagle Point, generating a clockwise circulation within the northern one-third of the lake. This understanding of the wind-driven currents indicates that poor water quality conditions (particularly low dissolved oxygen concentrations) that are observed in the northern part of the lake do not originate locally. Instead, these conditions originate farther south in the lake and are transported to the north along this circulation path through the trench and west of Bare Island (Wood and others, 2006).

In 2005, the existing water quality monitoring program expanded to become lakewide in Upper Klamath Lake and to include Agency Lake. These changes created a program better suited to establishing long-term status and trends of water quality dynamics and monitoring the suitability of water quality for protection of endangered species of fish living within the lakes.

Meteorological sites were established at four locations on land around the lake in addition to the two floating meteorological sites used in previous years, providing greater resolution of wind speed, wind direction, air temperature, and relative humidity. Additionally, collection of solar-radiation data at SSHR began in 2005. The additional wind data were used to improve the hydrodynamic model describing water movement in Upper Klamath Lake. The air temperature, relative humidity, and solar-radiation data were used to calculate heat transfer at the water surface in a heat transport model of Upper Klamath Lake (T.M. Wood, U.S. Geological Survey, unpub. data, 2006; Wood and Cheng, 2006).

Purpose and Scope

This report presents the results of water quality monitoring in Upper Klamath and Agency Lakes during 2005. Meteorological data, including wind speed and direction, air temperature, relative humidity, and solar radiation, are presented and used to describe wind patterns and their influence on circulation in Upper Klamath Lake. Dissolved nutrient concentrations are correlated with chlorophyll a concentrations, which serve as a surrogate for algal biomass. Results of dissolved oxygen production and consumption experiments are described. Dissolved oxygen concentration and saturation, water temperature, pH, and specific conductance values of water samples collected from the lakes are presented and used to determine water quality conditions potentially harmful to fish.

Description of Study Area

Upper Klamath Lake (fig. 2) is located in southern Oregon. It is a large, shallow lake 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 western shore of the lake. This trench contains the deepest waters of the lake, approaching 15 m. Upper Klamath Lake is located 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 contributes, on average, nearly one-half of the lake’s incoming water and enters the lake near its northern end. Upper Klamath Lake historically was eutrophic, but over the past several decades has experienced nuisance blooms of AFA during the summer and fall and can now be characterized as hypereutrophic (Eilers and others, 2004). Upper Klamath Lake is a natural water body, but lake-surface elevations have been regulated since 1921, when the 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 principal water source for the Klamath Project, an irrigation system developed to supply water to farms and ranches in and around the Klamath basin (Bureau of Reclamation, 2000).

Agency Lake, just north of Upper Klamath Lake and connected to it by a natural, narrow channel, adds about 38 km² of surface area to the Upper Klamath Lake-Agency Lake hydrologic entity (Johnson, 1985). Agency Lake also is shallow, with a maximum depth approaching 3 m and an average depth of 0.9 m. Like Upper Klamath Lake, Agency Lake is hypereutrophic and experiences annual blooms of AFA. Because the channel connecting Upper Klamath Lake and Agency Lake is narrow compared to the two water bodies and the amount of flow through it is small, the two lakes are largely independent in terms of the seasonal cyanobacterial bloom and water quality dynamics.

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