Pesticide warning signs are a common sight on eastern Maine blueberry barrens in spring and early summer, and the rains wash these pesticides into Maine's salmon rivers. Photo by Paul Donahue. Some registered 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 sea water.
U.S. 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. The agency's most recent study of the Willamette River Basin found pesticides at higher concentrations than earlier testing revealed. Salmon fry are particularly vulnerable to pesticides. NMFS has indicated serious concern about the effects of pesticides on salmon. Current EPA pesticide use requirements were developed in the absence of information about some of these subtle but real impacts on aquatic species such as salmonids.