The overall proportion of waterways in the United States where "concerning" level of pesticide runoff has been detected has more-or-less remained level, though pollution in urban areas has rocketed in the past decade, according to a 20-year study by the US Goeological Survey.

Though the proportion of waterways on agricultural and mixed use land where contamination occurred remained similar over the two decades, over 90 percent of urban streams were contaminated with "pesticides that exceeded an aquatic-life benchmark" between 2002 and 2011, compared to just over 50 percent the previous decade.

Pollution from agricultural land fell slightly over the second decade studied, but worrying levels of contamination were detected in almost two-thirds of streams and rivers into which farmland drains between 2002 and 2011.

Over 220 million kg of pesticides are used each year in the United States. Fipronil, an insecticide that disrupts the central nervous system of insects, and which was partially banned in the EU last year, was the pesticide most frequently found at levels of potential concern for aquatic organisms in urban streams during 2002-2011.

Researchers working on the survey noted that their findings likely underestimate the true level of pollution and its impact on the environment. They said, "The potential for adverse effects on aquatic life is likely underestimated in these results because resource constraints limited the scope of monitoring to less than half of the more than 400 pesticides currently used in agriculture."