Four million gallons of partially treated sewage poured into Long Island Sound over 24 hours ending Monday, August 3, from the same Mamaroneck wastewater plant that released more than half a million gallons less than two weeks earlier.

That's 7.5 times larger.

The discharge from the Mamaroneck Sanitary Sewer District Wastewater Treatment Plant dwarfs the 536,240-gallon spill on Tuesday, July 21, which forced the closure of Coveleigh Club Beach in Rye and prompted the Rye City Council to join a regional body pushing for infrastructure upgrades at the county-operated facility.

The plant, located at Harbor Island Park on Boston Post Road in Mamaroneck, attributed the release to weather conditions during a short-term wet-weather event, according to MyRye.com.

The wastewater was partially treated with disinfection before being discharged through a 60-inch outfall pipe that extends about half a mile into the Sound.

Impact on Rye beaches

Sewage from Rye homes flows to both the Mamaroneck plant and the Blind Brook treatment plant in Disbrow Park. When bacteria counts spike after a discharge of this size, the Westchester County Department of Health can close public and private beaches along the Sound shore, including Coveleigh Club at 459 Stuyvesant Avenue.

After the July 21 spill, the county health department closed Coveleigh Club Beach on Wednesday, July 22, along with beaches in Mamaroneck and New Rochelle, citing 0.73 inches of rainfall the prior day. The county uses rainfall thresholds to trigger closures: more than half an inch means a one-day closure, more than an inch means two days, and more than two inches triggers a closure of undetermined length.

No beach closure announcement specifically tied to the August 3 discharge had been posted as of Monday, August 3, though the county's social media accounts noted closures due to heavy rainfall on the same day.

A pattern of releases

The August 3 discharge marks at least the third major release from the Mamaroneck plant in 2026. The Rye City Council responded to the July 21 spill by joining a regional body to advocate for upgrades to the aging facility, as we reported in July. No public statement from Westchester County Executive Ken Jenkins or Health Commissioner Sherlita Amler specifically addressing the August 3 event has been released.

The disclosure was made under New York's 2013 Sewage Pollution Right to Know Act, which requires the state Department of Environmental Conservation to notify the public of sewage discharges so residents can avoid swimming, boating, or fishing in potentially contaminated water.

As of Monday evening, no county official had publicly addressed the second massive discharge in 13 days from the plant that handles Rye's wastewater.