Background Information on Pesticides and Salmon Facts About Pesticides, Salmon, and the Endangered Species Act Background Information on Pesticides and Salmon Pesticides have profound effects on Northwest salmon and may be a serious factor in their decline. The US Geological Survey has found concentrations of pesticides in Pacific Northwest rivers and streams at levels that are associated with negative impacts on fish growth, development, behavior, and reproduction.
Some pesticides are lethal to salmon, and large fish kills have occurred.
Pesticides can impair swimming ability, cause abnormal sexual development, and cause skeletal deformities. Pesticides can indirectly affect fish by changing the aquatic environment, by reducing the food supply, and by eliminating vegetative cover used by young salmon. Pesticides can impair salmon s ability to transition from freshwater to seawater. Since then, many salmon runs have declined because of a combination of many factors including too many dams and widespread habitat loss. One likely fact that has received little scrutiny, however, is the long-term impact of increasing uses of agricultural chemicals and pesticides in many Northwest river systems.