Kootenai River Biological Baseline Status Report : Annual Report, 1996.

Abstract

The Kootenai River ecosystem in Idaho, Montana and British Columbia (B.C.) Canada has been severely degraded during the past 50 years. This aquatic ecosystem has changed from one that was culturally eutrophic, to one that is oligotrophic due to channelization, diking, impoundment (construction and operation of Libby Dam), and pollution abatement measures in the watershed. As a result of these influences, flow regimes, temperature patterns, and water quality were altered, resulting in changes in primary production and aquatic insect and fish populations. Construction of Libby Dam (creation of Lake Koocanusa) and closure of Cominco`s fertilizer plant resulted in decreased phosphorus load to the Kootenai River to below historical levels. Dissolved orthophosphorus concentrations averaged 0.383 mg/L in 1970 as compared to 0.039 mg/L in 1979. Total phosphorus concentrations followed a similar pattern. Both total phosphorus and soluble reactive phosphorus concentrations remained below 0.05 mg/L from 1976 to 1994, characterizing the river as oligotrophic. Post Libby Dam primary productivity levels in the river represent an ultra-oligotrophic to mesotrophic system. Since the construction and operation of Libby Dam, invertebrate densities immediately downstream from the dam increased, but species diversity decreased. Insect diversity increased with increasing distance from the dam, but overall species diversity was lower than would be expected in a free-flowing river. Fish species composition and abundance has also changed as a result of the changes in the river and its watershed.