Water Quality Impacts

Water quality problems are the result of land use practices that affect streams basinwide, flows altered by dams and irrigation withdrawals, and discharge of pollutants from point sources. The major water quality issues related to anadromous fish production in the Columbia River Basin involve temperature, silt and sediment, dissolved gases and chemical pollution.


In portions of many rivers and streams throughout the Columbia River Basin, water temperatures commonly exceed lethal levels for salmonids during August (Collins 1963; Thompson 1974; Liscom et al. 1985; Vigg and Watkins 1991; Meyer 1989; Karr 1992). Water temperatures now commonly exceed 21oC (70oF) in the mainstem (Collins 1963; Shew et al. 1985; Meyer 1989). Systems affected (refer to adjacent Figure 3.3) include the Deschutes, John Day, Umatilla, Walla Walla, Yakima, Wenatchee, Entiat, Methow, Okanogan, Tucannon, Clearwater, Salmon, and Grande Ronde rivers; the Columbia River mainstem from the mouth to Chief Joseph Dam; the entire Snake River mainstem; and the Columbia River estuary.

These increased water temperatures equal or exceed levels that are lethal for Columbia River Basin salmon stocks which migrate during this time (Karr 1992). Duston et al. (1991) noted that increases in water temperature interfere with the ability of juvenile salmon to achieve smoltification. In addition “ecological death” as a result of loss of equilibrium occurs at even lower temperatures (Coutant 1970). Existing mainstem temperatures may also explain some of the variation in conversion rates (the difference in numbers at two consecutive dams after accounting for known losses) of steelhead stocks migrating through the lower reaches of the Snake River (Filardo 1990), and the failure of radio-tagged fish to pass upstream (Trefethen and Sutherland 1968; Stabler 1981; Shew et al. 1985). Migration delays caused by high temperatures have been observed often, particularly where tributary temperatures exceed those of the mainstem Columbia River (Major and Mighell 1966; ODFW 1977; Johnson et al. 1982; Liscom et al. 1985). Adult salmon may be further stressed by warmer waters in the reservoirs, and suffer prespawning mortalities (McGie 1992).

Silt and Sediment

The amount of silt and sediment entering streams and rivers can be increased by several orders of magnitude above background levels, as a result of human disturbance in the watershed (through logging, road construction, grazing, mining, and agriculture). Silt settles into coarse gravels, and decreases water circulation needed by salmon eggs in the gravels.

Dissolved Gases

Hydroelectric projects in the tributaries and mainstem have altered concentrations of dissolved gases in the basin. During periods of high runoff, entrainment of gases into dam tailraces caused by large volumes of water over dam spillbays can lead to gas bubble trauma. During warm periods, dissolved oxygen levels can become critically low in the bottom portion of reservoirs.


Runoff from agricultural fields, feedlots and urban areas, sewage treatment plant discharges, combined sewer overflows, and heavily grazed tributary streams contains nutrients that lead to excessive plant growth. This growth reduces the amount of oxygen available for aquatic life, and can create fatally anoxic conditions.

Toxic pollutants enter streams and rivers through industrial waste discharges, surface runoff from urban areas, and runoff from agricultural and forested land where herbicides and pesticides are applied. Heavy metal pollution may be generated by active or abandoned mining sites. These pollutants often reduce the supply of food available for salmon, and heavy metals directly decrease the survival of eggs and rearing fish.

According to the State of Oregon, all of the Columbia River within the state’s borders (river miles 0-309) is in violation of the state water quality standard adopted for dioxin (ODEQ 1994). Washington State has specifically identified the Columbia River mainstem downstream of Priest Rapids Dam and the entirety of the Snake River within Washington State as violating the dioxin water quality standard (WDOE 1992).

Organochlorine compounds that disturb the endocrine systems of exposed organisms adversely affect the development of the organism’s reproductive system and create immunological deficiencies. Contaminant exposure and uptake by fish can occur even when fish are in a contaminated area for a brief time and such exposure can trigger changes in enzyme levels and DNA damage (McCain et al. 1990). The effects of these chemicals may be exacerbated by near-lethal water temperatures which exist in the mainstem Columbia and Snake rivers at times during the summer (Collins 1963; Meyer 1989; Karr et al. 1992).

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