Rotenone in Fisheries: Are the Rewards Worth the Risks?

3. Knife Lake and Knife River Rehabilitation Project

Timothy J. Brastrup

doi: https://doi.org/10.47886/9781888569339.ch3

Abstract.—In October 1989, the Minnesota Department of Natural Resources (MNDNR) treated 1,266-acre Knife Lake and 70 miles of the Knife River system above the lake with a synergized rotenone concentrate formulation to eliminate the carp Cyprinus carpio population. This was a controversial project from initial planning through treatment, and required a lengthy mitigation process. Issues, such as environmental contamination, damage to endangered species, reduced lake-based recreation and economic loss, project cost, chemical toxicity, effects on nontarget organisms, and damage to cultural resources, were raised initially by two people in opposition. It required 18 months and the preparation of an Environmental Assessment Worksheet to mitigate or address these concerns. The mitigation process involved several MNDNR disciplines, various other units of government, and a large sportsmen’s organization. Because of the lengthy mitigation process, the cost increased from the planned $119,150 to $350,000. The results of the treatment were total removal of rough fish, improvements in water quality, reestablishment of aquatic macrophytes, and successful reintroduction of game fish. Walleye Stizostedion vitreum are again successfully spawning in the Knife River and numbers have greatly increased. Carp have not appeared in the watershed through 2000 and most of the pre-treatment fish assemblage has been reestablished. In a debriefing meeting following this project, MNDNR managers decided to take a pro-active approach to informing the public as a policy for future projects.