Researchers visited 186 streams and 5000 wells across the country. Every stream had at least one pesticide at some time, and 10% had levels that exceeded the benchmark at which human health effects are possible. The prevalence of pesticides was much lower in ground water; only 1.2% of wells exceeded the benchmark. There is more concern for aquatic organisms and the wildlife that feed upon them. Of the 178 streams near farms or cities, 56% had one or more pesticides exceeding benchmarks. “Aquatic life in urban streams is particularly threatened,” said report author Robert Gilliom, who leads the USGS’s Pesticide National Synthesis Project Study Team.