Rivers
CT Rivers Contain Neonics at Levels Deadly to Aquatic Insects
Mayfies are a key part of the food chain for many fish species.
Fifty-six percent of Connecticut rivers have neonics present at levels exceeding EPA benchmarks for aquatic life, according to a 2025 UConn report. Since insects are food for fish, amphibians, birds and other wildlife, neonics threaten to hollow out Connecticut’s aquatic ecosystems.
Overuse of Neonics on Lawns is Killing Beneficial Insects in CT Rivers
Neonics stand out as a unique threat to Connecticut’s river ecosystems. They are present in the state’s rivers at levels consistently exceeding EPA chronic exposure benchmarks for aquatic life, (UConn, 2025). The U.S. Geological Survey’s monthly monitoring of the Norwalk River shows, for example, that of 218 pesticides monitored annually, 30 show up in the river, and one–imidacloprid–shows up at levels deadly to aquatic life. Imidacloprid is a neonic used largely in Connecticut on turf grass to kill white grubs, a use studies show is ineffective (Clavit, 2014).
Surface water samples from the Norwalk River, collected by the U.S. Geological Survey between 2013 and 2023, were analyzed for the insecticide imidacloprid. These results are compared to the U.S. EPA chronic benchmark for aquatic invertebrates (0.01 µg/L). Samples exceeding this benchmark (>49%) are likely to cause harm to aquatic invertebrates with prolonged exposure.