PROJECT CHIEF: Kurt Carpenter
The Clackamas River in northwestern Oregon drains the western slope of the Cascade Range, descending from forested highlands into the Willamette Valley. The Clackamas River is an important source of drinking water, serving more than 200,000 people. The river and its tributaries also support diverse aquatic life, including resident and anadromous fish. Today, populations of spring Chinook salmon and winter steelhead trout in the Clackamas Basin are listed on the Endangered Species List as threatened by the National Marine Fisheries Service, and late-run Clackamas River coho salmon, the last remaining wild coho salmon stock in the Columbia River Basin, was listed as a candidate species in 1995.
Water quality in the Clackamas River is considered very good to excellent compared with that of other rivers in the State, based on the Oregon Department of Environmental Quality's Water Quality Index, and has withstood pressures from human impacts and natural disturbances seemingly well. In September 1994, however, foul tastes and odors appeared in drinking water supplied by the Clackamas River. A survey of the watershed for a potential cause of this problem indicated that an algal bloom had developed in North Fork Reservoir. Water samples collected from the reservoir contained Anabaena, a blue-green alga that is notorious for causing taste and odor problems in drinking-water supplies. Chemical analysis of the untreated and treated drinking water identified geosmin, a taste and odor compound that is produced by many blue-green algae and certain actinomycete bacteria.
Nuisance blooms of blue-green algae are fueled by excess nutrients, and their presence may be an indication that eutrophication, the process of nutrient enrichment, is occurring. Other signs of eutrophication, such as high algal biomass in streams, also have been observed in the Clackamas River and some of its tributaries. During the spring of 1996, moderate-to-heavy growths of green algae were observed in the Clackamas River and some of its tributaries, including Fish Creek and the Oak Grove Fork. Declines in water quality that can result from such blooms, including taste and odor problems, increased concentrations of toxic disinfection by-products in drinking water, low levels of dissolved oxygen, and high pH, are beginning to appear in the Clackamas River.
To address this issue, in 1995 the U.S. Geological Survey (USGS), with the cooperation of local water providers and county and State agencies, initiated a water-quality investigation. This effort was expanded in 1998, when a basinwide survey of nutrients, algae, and basic water quality (temperature, dissolved oxygen, and pH) was conducted (Carpenter, 2002). During 2000-01, water-quality monitors were installed in the Clackamas River (downstream of River Mill Dam near Estacada at river mile 23 and in the lower river near Oregon City). These monitors provide near-real-time data on temperature, dissolved oxygen, pH, conductance, turbidity, and chlorophyll (at Oregon City only), and can be accessed at http://oregon.usgs.gov/clackamas/monitors/.
In 2000-01, the USGS collected samples of storm runoff from the lower Clackamas River and its tributaries for pesticides. During 2003, samples of untreated Clackamas River water used for drinking were analyzed for numerous contaminants, including pesticides, volatile organic compounds, and various wastewater compounds such as caffeine, hormones, pharmaceuticals, and other compounds.
Clackamas River Water Quality Monitors
Data from 2000-01 lower Clackamas River Basin pesticide study used in Carpenter (2004), above (Excel table)
Contact: info-or@usgs.gov
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