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A deceased fish on the side of the Potic Creek.

Department of Environmental Conservation personnel collect dead fish on the Potic Creek in Coxsackie, N.Y. on Aug. 8, 2022.

A pump truck clears out tanks and holding pools at the Catskill Water Treatment Plant.

COXSACKIE — About 1,500 gallons of a water-treatment chemical spilled near the Potic Reservoir, the source of drinking water for the village of Catskill, on Sunday, killing hundreds of fish in the Potic Creek downstream from the reservoir.

The chemical — aluminum salts, or alum — is used in municipal reservoirs to improve the clarity and purity of the water. When properly dispersed, the alum particles bind with phosphorus particles — which can cause blue-green algae blooms — making them insoluble in water and causing them to sink to the reservoir's bottom. Alum also tends to drag down particulate matter, improving the clarity of the water.

The alum spilled because of a cracked fitting on a pipe, according to Catskill Department of Public Works Superintendent Robert Young. The material then flowed into the Potic Creek downstream of the reservoir, meaning the water source was not affected, Young said. The faulty pipe had been fixed and isolated on Sunday, he added.

The state Department of Environmental Conservation, which is overseeing the cleanup, confirmed that no alum from the spill had entered the reservoir. "There has been no impact on public drinking water at all," DEC spokesperson Jomo Miller said.

A DEC Emergency Management unit was on scene Monday morning to clean up approximately 300 dead fish, which were found as far as a half-mile from the spill.

The Potic Creek is a tributary of the Catskill Creek, which is itself a tributary of the Hudson. The Catskill Creek is stocked with trout from DEC hatcheries, but the Potic Creek was probably too warm and intermittent to support trout, Trout Unlimited Engagement Coordinator Jesse Vadala said.

The organization's concern was whether "even trace amounts" of alum made it into the Catskill Creek or the Hudson River. But months of dry weather in the region appeared to be helping the pollution stay put. On Monday morning, the Potic Creek was low, with runnels, or narrow channels, connecting pools of still water.

The village is cleaning up impacted backwash water from its settling ponds to make sure it is not discharged, which would further impact the creek, according to the DEC. A truck from a septic company was seen working at the water treatment facility on Monday.

The DEC's investigation "is ongoing and will determine any potential enforcement or long-term remedial actions," the agency said. Personnel "will continue to oversee the cleanup until it is complete and the public and the environment is protected." 

Alum does not bio-accumulate, according to the DEC, so wildlife that may have eaten the dead fish will not be sickened.

Roger Hannigan Gilson covers Columbia and Greene counties for the Times Union. He has worked as a reporter in the northern Hudson Valley since 2014 and spends most of his additional time outdoors. Drop him a note at roger.hannigangilson@timesunion.com.