Evaluation of Water and Nutrient Balances for the Upper Klamath Lake Basin in Water Years 1992-2010.

Upper Klamath and Agency Lakes (UKL) comprise a large, shallow, hypereutrophic lake system located in south-central Oregon that is seasonally dominated by large blooms of the nitrogen-fixing cyanobacterium Aphanizomenon flos-aquae. Bloom-driven water quality degradation that includes extended periods of low dissolved oxygen, elevated pH, and toxic levels of un-ionized ammonia has been associated with the decline of native endangered fish populations, including the Federally Listed shortnose (Chasmistes brevirostris) and Lost River (Deltistes luxatus) suckers. More specifically these conditions have been linked to large die-offs and redistribution of the endangered sucker species in UKL. Several studies have documented that recurring algal blooms and their decline are associated with periods of elevated pH, toxic levels of un-ionized ammonia, and depressed dissolved oxygen concentrations. Based on exceedances of water quality standards for dissolved oxygen, pH, and chlorophyll (algal biomass), both lakes were designated as water quality limited for resident fish and aquatic life.