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Klamath Falls Field Station

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Upper Klamath Lake Water Quality

Impaired water quality conditions in Upper Klamath Lake have been implicated in reduced survival of fishes and are a concern for recovery efforts. Upper Klamath Lake is the largest lake in Oregon (280 km2), but is relatively shallow (average depth about 2 meters). The combination of this bathymetry with a watershed naturally enriched in phosphorus has led to the conclusion that the lake has been eutrophic since the earliest records in the mid-1800s. Water quality in Upper Klamath Lake, however, has been markedly altered from those historical conditions by various human activities in the watershed, particularly the drainage of marshes and wetlands, timber harvest, and water control and allocation related to agricultural development. These changes have created a hypereutrophic system that experiences massive phytoplankton blooms dominated by a single cyanobacterium, Aphanizomenon flos-aquae. High pH levels and supersaturated dissolved oxygen concentrations result from photosynthetic processes during A. flos-aquae blooms in the summer and fall. Rapid cell senescence of the bloom during peak summer water temperatures result in extremely low dissolved oxygen concentrations. Both high pH and low dissolved oxygen concentrations are associated with mortality of fishes and can lead to large-scale fish die-offs. In addition, the hepatotoxin-producing cyanobacterium Microcystis aeruginosa blooms in Upper Klamath Lake as A. flos-aquae senesces. Microcystin, the toxin produced by this cyanobacterium, is found in concentrations exceeding the World Health Organization limit for drinking water (1μg/L) in Upper Klamath Lake in mid- to late summer. Ongoing research at KFFS seeks to determine the possible effects of this toxin on the health and survival of endangered fishes.

Photo of cyanobacteria bloom

Upper Klamath Lake cyanobacteria bloom.
Photograph by U.S. Geological Survey

Photo of cyanobacteria bloom

Upper Klamath Lake cyanobacteria bloom.
Photograph by U.S. Geological Survey

Link of interest

Long-Term Water Quality Monitoring Program in Upper Klamath Lake, Oregon

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