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Spokane River snippet

Spokane dissolved oxygen TMDL

What are the Water Quality Concerns?

The Spokane River and Lake Spokane have low dissolved oxygen (DO) levels during low flow in the summer months. Portions of the river and Lake Spokane violate the Washington State water quality standards for DO, and are listed on the 2008 list of impaired water bodies.

Maintaining good water quality in the river, especially adequate concentrations of DO, is vitally important for supporting fish, invertebrates and other aquatic life.

The following graphic was taken from the Spokane River DO TMDL modeling and shows how DO decreases in Lake Spokane (Long Lake) throughout the year. Cold water fish, such as trout (salmonids), generally prefer DO in the “green” range of the graphic. Click on the graphic to watch the change in DO levels for spring – fall 2001. Note the onset of “blue” or low DO water in the summer months and the reduction of green in the deeper parts of the lake, where salmonids will try to take refuge in the hot summer months. Low dissolved oxygen in the lower depths of the lake in summer effectively reduces the volume of habitat available to salmonids.

Graph of dissolved oxygen levels in Long Lake in Washington State, 5/16/2001.  Provided by David Moore, WA Department of Ecology

In addition to being required by aquatic organisms for respiration, oxygen is necessary to help decompose organic matter in the water and bottom sediments. It is also necessary for other biological and chemical processes.

What affects DO levels?

Sources of Oxygen-Consuming Substances (BOD) and Nutrients

Why this matters


See our Frequently Asked Questions for more information about this TMDL. (Ecology Publication)


Last updated May 2016