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Salmon and Clearwater Basins Aquatic Biology Assessment


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Some streams naturally exceed water temperature standards set by the Idaho Department of Environmental Quality (IDEQ). Yet some of these streams appear to support cold-water aquatic life. IDEQ needed a better understanding of the normal range of Idaho stream temperatures and the relationships between aquatic life and stream temperature.

The Salmon and Clearwater River basins, large areas of which are relatively undisturbed by human activities, provide an ideal setting to determine the most important factors controlling stream temperature.

Owl Creek.
Owl Creek, photo by USGS.

How the USGS Helps

Our scientists monitored stream temperatures hourly for about 60 days during July, August, and September 2000 at sites in relatively undisturbed rivers and streams in the Salmon and Clearwater River basins in central Idaho. The monitored sites and the hydrologic subbasins they represented varied widely in size, elevation, drainage area, and vegetation cover. Scientists analyzed the data for statistical correlations with basin and site characteristics to establish the most important factors affecting stream temperature.

Environmental variables (with a focus on stream temperature) and benthic invertebrate and fish assemblages were evaluated for 34 streams in the Salmon River basin during July through September 2001. Data were collected to document the thermal regime of least-disturbed streams, to characterize the distribution of aquatic biota in streams representing a gradient of temperature, and to describe the relationships between the environmental variables and the benthic invertebrate and fish assemblages.

Key Findings

  • Stream temperature varied substantially among sites withing the basin.
  • Stream temperatures exceeded criteria for bull trout and chinook salmon spawning at all sites.
  • Many nutrient concentrations in water samples were relatively low.
  • We identified 201 benthic invertebrate taxa from the 34 sampling sites, including coldwater species collected from sites where temperatures exceeded the IDEQ criteria for the protection of coldwater biota.


Ott, D.S. and Maret, T.R., 2003, Aquatic assemblages and their relation to temperature variables of least-disturbed streams in the Salmon River basin, central Idaho, 2001: U.S. Geological Survey Water-Resources Investigation Report 03-4076, 45 p.