A decade-long federal monitoring push has found pesticides repeatedly turning up in rivers across the Midwest and Great Plains, sometimes at concentrations likely to harm aquatic plants and insects. The pattern runs from corn country into urban streams, putting pressure on utilities, farmers and regulators to deal with wet weather spikes and contamination that lingers.
The U.S. Geological Survey's national data release tracked 84 pesticides at 81 long-term stream sites during water years 2013 to 2022 and turned up some troubling results. At most sites, at least one pesticide reached concentrations that could hurt aquatic life, and 19 pesticides exceeded EPA aquatic life benchmarks. Two thirds of the monitored sites saw exceedances of at least one acute and one chronic benchmark, with atrazine standing out as the most common acute exceedance and imidacloprid as the most frequent chronic exposure. The sampling is part of the USGS National Water Quality Network and is designed to spotlight long-term trends rather than short storm-driven spikes, according to the U.S. Geological Survey.
“This is the largest consistently monitored nationwide network,” said Megan Shoda, a USGS hydrologist and one of the study's authors, who added that “this sampling at this rate is likely underestimating real conditions.” The study flagged atrazine, metolachlor and imidacloprid as top threats to clean water, and reported acute atrazine detections at places such as the Kansas River at De Soto and the White River near the Indiana-Illinois border. Imidacloprid exceeded chronic or acute levels in rivers including the Brazos south of Houston, Shingle Creek in Minneapolis and the North Canadian River near Oklahoma City. The Environmental Working Group's Tap Water Database shows atrazine detected in more than 2,000 utilities that together serve roughly 40 million people, as reported by Harvest Public Media.
Regulatory Gaps And International Context
The U.S. federal regulatory framework still has notable gaps. The EPA has not set an enforceable maximum contaminant level for imidacloprid in public water supplies, a shortcoming called out in state guidance such as Wisconsin's review of pesticide drinking water standards, according to the Wisconsin Department of Natural Resources. European regulators, by contrast, removed atrazine from the market years ago and in 2018 moved to prohibit most outdoor uses of neonicotinoids, including imidacloprid, under rules from the European Commission.
What Scientists Say
Aquatic ecologists warn that a mix of chemicals in the water can magnify damage. “They have the same effect in the water,” said Debbie Baker, an aquatic ecologist at the Kansas Biological Survey, explaining that harming plants or insects can ripple up the food chain and cut oxygen levels and habitat for other species. Scientists also stress that routine sampling can miss short storm-driven surges in concentrations, which means the measured averages probably understate peak exposures. The reporting was detailed by Harvest Public Media.
Local regulators, utilities and farmers are already weighing what to do next, from more frequent monitoring to targeted vegetated buffer strips and changes in pesticide timing to limit runoff. Residents who want to check local results can look up their utility's annual water quality report or search the Environmental Working Group's Tap Water Database to see whether atrazine or other pesticides have been detected in their system. For further reading, see the U.S. Geological Survey data release and the Environmental Working Group Tap Water Database.
