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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5117

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Introduction

Upper Klamath Lake is a large (232 km²), relatively shallow lake located in southern Oregon, 25 km north of the Oregon-California border (fig. 1). Most of the lake is less than 4 m deep except for the narrow trench on the western edge of the lake. This trench, which runs parallel to Eagle Ridge, can be as much as 15 m deep. Just north of Upper Klamath Lake and connected by a narrow channel is Agency Lake, a smaller (37 km²) but equally shallow lake that is distinct from Upper Klamath Lake, both hydrologically and in terms of water quality. The primary contributor of inflow to Upper Klamath Lake is the Williamson River, which enters the lake near its northern end, east of the Agency Lake inflow, and accounts for about 46 percent of the lake’s incoming water (Johnson and others, 1985).

Lake surface levels are regulated by the Link River Dam, built at the southern outlet of the lake in 1921 by the Bureau of Reclamation. During construction of the dam, the rock sill that held Upper Klamath Lake was removed and replaced with the Link River Dam. As a result, the minimum possible post-dam lake level is about 1 m lower than the minimum possible pre-dam level. Area demands for water during summer months result in declines in lake level from May to September. At the median May lake level of 4,143 feet above sea level, the volume of water contained in the lake is 1,080 cubic hectometers (875,000 acre-feet). In contrast, the volume of water in the lake at the mean summer lake level of 4,141.3 feet is 765 cubic hectometers (620,000 acre-feet) [Snyder and Morace, 1997]. Water is diverted upstream of the lake for agricultural use and downstream to supply the irrigators of the Klamath Project, an irrigation system developed to supply water to 970 km² of farm and ranch land in and around the Upper Klamath basin. To meet the National Marine Fisheries Service flow requirements for Klamath River coho salmon (National Marine Fisheries Service, 2002), water is sent downstream through the Link River. Lastly, evaporation from the lake also results in a loss of water in the lake itself. It is difficult to balance these competing demands for water from the lake.

The lake was historically eutrophic but has become hypereutrophic, in large part due to land-use practices in the basin (U.S. Fish and Wildlife Service, 1993). As a result, the algal assemblage of the lake has shifted to a monoculture of the blue-green alga Aphanizomenon flos-aquae (AFA), massive blooms of which have been directly related to episodes of poor water quality in Upper Klamath Lake (poor conditions are defined as those that have the potential to be harmful to the endangered sucker species). The lake has experienced nuisance blooms of AFA during summer and fall for the past 40 years. The growth and decomposition of dense algal blooms frequently cause extreme water-quality conditions characterized by high pH (9–10.5), widely variable dissolved oxygen (anoxic to supersaturated), and high ammonia concentrations (greater than 0.5 mg/L, un-ionized) [Wood and others, 2006]. Severe water-quality problems in Upper Klamath Lake have led to critical fishery concerns for the region (Perkins and others, 2000).

In 1988, the U.S. Fish and Wildlife Service (USFWS) listed two species of suckers endemic to the lake as endangered: the Lost River sucker (Deltistes luxatus) and the shortnose sucker (Chasmistes brevirostris). Poor water-quality conditions associated with the long and productive blooms of AFA are believed to be the primary threat to adult endangered suckers. According to Ronald Larson (U.S. Fish and Wildlife Service, written commun., 2006), “of all the factors that might affect water quality in the short term, elevations [or lake level] are the only one we have some control over.”

Purpose and Scope

In 1996, Wood and others (1996) evaluated water-quality data collected by the Klamath Tribes from Upper Klamath and Agency Lakes for relations between water-quality conditions and lake level. At that time, data were available only for 1990 through 1994. The Tribes have continued to collect data and a comparable dataset is now available for 1990 through 2006. The Bureau of Reclamation asked the U.S. Geological Survey to update the original analysis performed by Wood and others (1996) with this larger dataset. In addition to the univariate approach used in the previous analysis, multivariable analyses will be assessed with this larger dataset and evaluated using an information-theoretic approach. These two approaches to the data analysis offer a chance to explore the data in a purely empirical manner unhampered by preconceived notions and an opportunity to use some of the knowledge developed since the initial analysis to inform a more in-depth evaluation of the data.

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