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

Table of contents || Previous section || Next section

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.

• Pollution sensitive native fish, such as cutthroat trout and torrent sculpin, were found predominantly in forested streams with large riffle areas, high quality riparian habitat, and low water temperatures. No external anomalies were found on fish from these streams.
• Pollution tolerant introduced fish, such as carp and bullheads, were collected primarily from streams with few riffles, poor quality riparian habitat, and high water temperatures. External anomalies were most abundant on fish from these streams.
• Relative abundances of fish generally were not highly correlated with water chemistry; however, pollution tolerant native fish, including minnows and reticulate sculpin, were found mostly in agricultural and urban streams with the highest nutrient and pesticide concentrations. External anomalies were moderately high on fish from these streams.

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

• Suspended sediment transport has remained unchanged downstream from 10 dams since their construction, but average particle size of the transported sediment has decreased. These facts indicate that erosion has increased downstream from the dams to compensate for the sediment trapped by the reservoirs.
• Erosion of stream channels and/or recently developed land could account for much of the sediment presently transported downstream from the dams.

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

• Fifty pesticides were detected in streams, and 10 pesticides exceeded criteria established by the USEPA for the protection of freshwater aquatic life from chronic toxicity.
• Atrazine exceeded the drinking water MCL of 3 µg/L (micrograms per liter) in one sample, and simazine exceeded the MCL of 4 µg/L in a different sample from the same stream; however, the stream was not used as a source of drinking water.
• Atrazine, simazine, metolachlor, deethylatrazine, diuron, and diazinon were detected in more than one-half of stream samples. Their concentrations varied seasonally in response to runoff and application rates.
• Forty-nine pesticides were detected in streams draining predominantly agricultural land, whereas 25 pesticides were detected in streams draining mostly urban areas. The highest pesticide concentrations generally occurred in streams draining predominantly agricultural land.
• In streams of the Pudding Basin, concentrations of atrazine, simazine, and metolachlor during spring runoff increased as the percent of drainage area in agriculture increased.

(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).

• Dinoseb (an herbicide) exceeded the MCL of 7 µg/L in ground water from one shallow domestic well, and tetrachloroethene (a VOC) exceeded the MCL of 5 µg/L in a second well. These were the only organic compounds detected at concentrations greater than USEPA drinking water MCLs in domestic wells.
• Pesticides were detected in water from about one-third of the shallow alluvial wells sampled, but concentrations typically were low. A greater variety of pesticides was found at higher concentrations in agricultural areas than in urban areas.
• VOCs were detected in water from about 20 percent of the shallow alluvial wells sampled. VOCs were found more frequently in urban areas than in agricultural areas.

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

• Concentrations of total dioxins and furans in bed sediment from streams and lakes exceeded the USEPA guideline for risks to fish at 2 of 22 sites; both sites were downstream from industrial areas. Concentrations in fish tissue did not exceed the threshold for risks to predator fish at any of the 8 sites where fish were collected.
• Dioxin and furan concentrations in bed sediment from forested and agricultural basins are similar to those found in other areas of the United States where atmospheric deposition is the presumed source.

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 in bed sediment exceeded USEPA guidelines for protection of aquatic life at 10 of 47 sites. Chlordane and its component compounds, and DDT and its degradation products accounted for most guideline exceedances.
• Concentrations in fish at 17 sites did not exceed National Academy of Sciences and National Academy of Engineering criteria for protection of fish-eating wildlife.
• The most commonly detected organochlorine compound both in bed sediment and aquatic biota was p,p'-DDE, a degradation product of DDT.

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).

• Chromium and nickel, which are relatively abundant in Willamette Basin rocks, commonly exceeded guidelines.
• The highest concentrations of cadmium, lead, silver, and zinc in bed sediment were in urban streams.
• The highest mercury concentrations in bed sediment were downstream from an abandoned mercury mine. High mercury concentrations in fish have prompted the Oregon Health Division to issue advisories warning of health risks from consumption of fish taken from some streams and reservoirs.

U.S. Geological Survey Circular 1161

|| Table of contents || Previous section || Next section