How Lawn Chemicals Affect Oyster Health

According to reports from the University of Connecticut, the Connecticut shellfish industry cultivates over 70,000 acres of coastal waters, generating $30+ million in annual economic impact. The thriving sector supports nearly 500 jobs across roughly 40 commercial producers, harvesting approximately 20 million oysters and clams every year.

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Connecticut ranks among the top five shellfish-producing states nationwide and third on the U.S. Atlantic coast. The industry is a vital part of the shoreline economy, marked by these specific metrics

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Copps Island oysters, at the mouth of the Norwalk River, is one of the most robust oyster companies in the state.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Chemicals used to kill lawn grubs or other pests readily run off into streams and the Sound during rainfall. These neurotoxins and chemicals can severely harm aquatic invertebrates—the insects in rivers that form the base of aquatic food chains and help keep rivers healthy, working ecosystems. Studies show that common pesticides can decrease larval swimming activity, impair growth, and lower nutritional health.

 

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NRWA and partners at CT Pesticide Reform worked to help pass a 2025 law banning the use of these highly toxic chemicals on lawns—though they are still allowed on trees, shrubs, and agricultural products, including nursery plants. Neonics are known for their contribution to the ‘insect apocalypse’ and the loss of 3 billion birds over the last half century, but they also damage the health of shrimp and oysters, according to two new studies (1, 2) published by Australian researchers. Although this class of chemicals is best known for its hazardous impacts on pollinator populations, it is becoming increasingly clear that the entire food chain is at risk from continued neonicotinoid use. This study builds on an already established body of literature showing these systemic chemicals poison waterways, and this UConn study shows links between increases in neonics in the Norwalk River and declines in mayfly populations.

 

 

The primary use of neonics on lawns has been to treat grubs, beetle larvae that can damage the roots of turfgrass. Grubs, however, are becoming resistant to neonics, and landscape companies, golf course managers, and others have been replacing them with diamides, another class of synthetic, systemic insecticides. Diamides are less toxic to bees than neonics, but more toxic to butterflies and moths, and come with an EPA label warning of toxicity to aquatic insects, oysters and shrimp. Shellfish Commissioners from across the state have called for more testing on the diamide, chlorantraniliprole, to determine its effects on the growth and recruitment (attaching to oyster beds) of larval oysters.

 

 

Ironically, while vulnerable to pollution from stormwater runoff, healthy populations of shellfish actively provide vital environmental benefits to clean water. By filter-feeding, mature oysters consume excess nitrogen caused by lawn fertilizers and help reverse water-quality degradation. You can explore the NOAA Nutrient Removal Calculator to see the exact amount of nitrogen— from fertilizers and other runoff—removed by commercial oyster beds and clams.