Water Quality in the Willamette Basin, Oregon, 1991-95

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Summary of Major Issues and Findings in the Willamette Basin

Location map of the study unit

Water quality issues were identified at the start of the National Water-Quality Assessment of the Willamette Basin (Wentz and McKenzie, 1991). The findings summarized below represent our contribution to an increased understanding of these issues.

Relative abundances of fish species correlated best with instream and riparian habitat quality (p. 8-9). Habitat and fish communities in agricultural and urban streams were degraded compared with those in other NAWQA Study Units (p. 21).

Photo of stream (22,834 bytes)

Erosion has increased downstream from dams (p. 10).

Ground water/surface water interactions are significant in large, gravel-bed rivers (p. 11).

  • Dye injection studies and streamflow measurements demonstrate the widespread occurrence of significant ground water/surface water interactions in large, gravel-bed rivers.
  • Interchange of water between streams and adjacent aquifers can result in changes to associated nutrient and pesticide concentrations.

Photo of dye injection study (35,012 bytes)

Nutrients in streams and ground water are degrading water quality (p. 12-13).

  • In 45 percent of streams sampled, total phosphorus concentrations exceeded 0.1 mg/L (milligram per liter), which is the maximum value cited by the U.S. Environmental Protection Agency (USEPA) as a goal for prevention of nuisance plant growth.
  • Sixty-eight percent of streams where total phosphorus concentrations exceeded 0.1 mg/L drained predominantly agricultural land.
  • Guidelines do not exist for evaluating the effects of nitrate concentrations on algal growth, but nitrate concentrations in only 2 of 51 of streams exceeded the 10 mg/L maximum contaminant level (MCL) established by the USEPA for drinking water. Neither stream was used as a source for drinking water.
  • In streams of the Pudding Basin, nitrate and soluble reactive phosphorus concentrations during spring runoff increased as the percent of drainage area in agriculture increased.
  • Nitrate concentrations in ground water exceeded the USEPA MCL in 6 of 70 shallow domestic wells drawing water from the alluvial aquifer of the Willamette Valley.
  • Nitrate concentrations were higher downgradient from irrigated agricultural areas than from nonirrigated agricultural areas.
  • Nitrate concentrations in ground water are likely to increase in the future because water sampled as part of the present study entered the ground water system when nitrogen fertilizer application rates were lower than in subsequent years.

Photo of algal growth on stream (41,075 bytes)

Pesticides in streams are degrading water quality (p. 14-15).

Photo of tractor (22,238 bytes)

Ground water quality generally has not been degraded by pesticides or volatile organic compounds (VOCs) (p. 15). Radon and dissolved solids concentrations and pesticide detection rates were low when compared with other NAWQA Study Units (p. 22-23).

Dioxins and furans were detected in all bed sediment and fish tissue samples, including those from forested reference basins (p. 16-17).

Although they have been banned since the late 1980s or earlier, organochlorine pesticides and PCBs are still present in bed sediment and aquatic biota from streams and lakes (p. 18).

Concentrations of trace elements in bed sediment from streams and lakes exceeded Environment Canada draft guidelines for protection of aquatic life at 26 of 52 sites (p. 18-19); however, concentrations generally were low when compared with other NAWQA Study Units (p. 21).

U.S. Geological Survey Circular 1161

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Suggested citation:
Wentz, Dennis A., Bonn, Bernadine A., Carpenter, Kurt D., Hinkle, Stephen R., Janet, Mary L., Rinella, Frank A., Uhrich, Mark A., Waite, Ian R., Laenen, Antonius, and Bencala, Kenneth E., 1998, Water Quality in the Willamette Basin, Oregon, 1991-95: U. S. Geological Survey Circular 1161, on line at <URL:>, updated May 20, 1998 .

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Last modified: Tue Aug 18 10:45:44 1998