Each year, researchers from the state departments of Agriculture and Ecology measure how much of the pesticides used in farms and urban areas end up in surface waters.
Hector Castro with the Department of Agriculture says they use the report to make sure that pesticides are being used in ways that won't hurt the environment.
Pesticides leave traces that remain in the water for years.
The closest streams monitored in the report are in the lower Skagit-Samish watershed area.
Scientists also found that most pesticides showed up at concentrations below levels of concern for aquatic species.
The full report is available at http://www.ecy.wa.gov/programs/eap/toxics/pesticides.htm