USGS Home
Contact USGS
Search USGS

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

Back to Table of Contents

Summary and Conclusions

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 alga) Aphanizomenon flos‑aquae (AFA) during summer, massive blooms of which have been directly related to episodes of poor water quality in Upper Klamath Lake. 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.

The U.S. Geological Survey (USGS) began monitoring water quality in Upper Klamath Lake in 2002 in cooperation with the Bureau of Reclamation to supplement data collected previously by the Klamath Tribes since 1990. During 2002-04, the USGS water quality monitoring program study area was limited mostly to the northern one-third of Upper Klamath Lake. In 2005, the existing water quality monitoring program expanded to become lakewide in Upper Klamath Lake and to include Agency Lake.

Data from multiparameter continuous water quality monitors, physical water samples, and meteorological sites were collected from Upper Klamath and Agency Lakes, Oregon, in 2005 to assess water quality conditions and processes. The data show that the significant factors controlling water quality processes included AFA dynamics, lake bathymetry, and wind speed.

Diel photosynthesis–respiration processes and the seasonal pattern of changes in AFA biomass (inferred from chlorophyll a concentrations) lead to variation in dissolved oxygen, orthophosphate, and ammonia concentrations; pH; and specific conductance values. In previous years, AFA biomass increased markedly, then sharply declined, resulting in low dissolved oxygen concentrations and release of nutrients to the water column. In 2005, chlorophyll a concentrations increased in early July and then sharply declined during late July–early August. Daily medians calculated for all sites in Upper Klamath Lake show seasonally increased dissolved oxygen concentrations coinciding with an increase in pH in early July, followed by a decrease in dissolved oxygen concentrations and pH values and an increase in specific conductance values in late July–early August. In addition, orthophosphate and ammonia concentrations increased during the bloom decline in late July–early August. These water quality changes coincide with the AFA bloom in early July and decline in late July–early August. The inverse relation of specific conductance with dissolved oxygen concentration and pH observed from mid-July through early August in Upper Klamath Lake was attributable to the release of ionic nutrients from decaying AFA cells during the bloom decline.

Qualitative observations of the AFA bloom, verified by chlorophyll a concentration data provided by the Klamath Tribes, were directly related to patterns observed in dissolved oxygen concentration and pH in Agency Lake. Differences in water quality patterns observed between Upper Klamath Lake and Agency Lake were attributable to differences in bloom dynamics between the two lakes. Variability in specific conductance at sites near rivers and wetlands in Agency Lake and Upper Klamath Lake suggests that these influent waters may locally influence specific conductance.

In dissolved oxygen production and consumption experiments, the maximum observed dissolved oxygen production was 1.47 milligrams per liter per hour of oxygen, and the maximum observed dissolved oxygen consumption was –0.73 milligrams per liter per hour of oxygen. Dissolved oxygen production in the upper water column declined through July and recovered through August. The observed pattern was similar to that of dissolved oxygen concentrations measured by continuous water quality monitors in the lake during this time. In addition to seasonal changes, photosynthesis and respiration processes affect the timing of the daily extreme water quality parameters. At shallow sites, the daily extreme water quality parameter readings occurred during relatively well-defined time intervals linked to diel patterns of sunlight and solar heating. These time intervals became broader and less well defined at deeper sites as a result of the increased potential for water column stratification.

Coupled with AFA dynamics, wind speed and temperature variations also effect diel changes in dissolved oxygen concentrations in Upper Klamath Lake. In response to episodes of low wind speed or to a deep-water-column configuration, the lower portion of the water column can be independent from the upper column and more susceptible to oxygen consuming biological processes that lower dissolved oxygen concentrations.

Bathymetry was the primary factor influencing the magnitude of the seasonal pattern of dissolved oxygen concentration at the deepest and shallowest monitoring locations around Upper Klamath Lake. Wind-driven circulation patterns determined the degree to which the seasonal extremes occurred at sites of similar depth that were either northwest or south and east of the trench under the prevailing clockwise circulation pattern. Because the northern part of the lake (preferred habitat for adult suckers) receives waters from the trench under the dominant circulation pattern, the monitoring sites there tended to record lower seasonal minimums of dissolved oxygen concentration than did the sites in the lake that are south and east of the trench. These factors also influenced shorter timescale dynamics of dissolved oxygen concentration, as evidenced by a mass of water with a low dissolved oxygen concentration that was first observed in the trench and migrated to subsequent sites along the dominant flow path during a period of 1–2 days. This event illustrates how oxygen-depleted water emerging from the trench is re-oxygenated as it travels through shallower areas in the northern part of the lake.

Monitoring water quality parameters (temperature, dissolved oxygen concentration and saturation, pH, and un-ionized ammonia concentration) allowed identification of the extent and duration of conditions potentially harmful to fish. Although high temperatures may have caused stress to fish and other aquatic species during the 2005 study, water temperatures never exceeded the critical value of 28ºC in Upper Klamath Lake. Periods of dissolved oxygen concentrations potentially harmful to fish were largely confined to the trench and a few sites in the northern part of the lake and were not persistent. On two occasions pH values potentially harmful to fish occurred within a significant portion of Upper Klamath Lake, but the data showed that these values were not persistent. Un-ionized ammonia did not reach concentrations potentially harmful to fish.

The expanded network of continuous water quality monitoring sites, physical water samples, and meteorological sites provided information critical to understanding lakewide water quality dynamics in Upper Klamath Lake. The network provides a greater awareness of water quality conditions in relation to circulation and water column stratification patterns and is central to future water quality modeling efforts. Continued operation of the monitoring sites to collect a long-term data set also would enable the identification of water quality status and trends in Upper Klamath Lake. Future monitoring would be enhanced by the addition of two sites to better quantify conditions surrounding the trench. One of the new sites would best be located between sites MDL and MDT, and the other between sites EPT and MDN, to better quantify the differences in algal dynamics between these sites.

Atmospheric conditions were monitored at meteorological sites over and around Upper Klamath Lake. Patterns of air temperature and relative humidity were consistent with the hot, dry summers typical of the Upper Klamath Lake basin. Wind speed and direction measurements showed significant differences in wind patterns around the lake, particularly between the northern part of the lake and areas to the south. The finer resolution of meteorological conditions in and around Upper Klamath Lake provided by these meteorological sites will improve water quality modeling results and enhance understanding of water quality dynamics in Upper Klamath Lake.

Back to Table of Contents