Long Island Sound water quality improving, nonprofit Save the Sound says, but there's more to be done

Water quality in Long Island Sound appears to be improving, according to testing by the nonprofit Save the Sound, but many bays showed poor levels of oxygen needed to sustain marine life. 

The organization released a report card for Long Island Sound Tuesday. It tested samples of the open water for nitrogen levels that indicate human activity and looked at trends in the bays on Long Island and in Connecticut.

The report found 98% of open waters in Long Island Sound scored a grade of B or better, said Peter Linderoth, director of healthy waters and lands for Save the Sound. 

Save the Sound, scientists with Cornell Cooperate Extension of Suffolk County Marine Program and elected officials discussed the results Tuesday at Gold Star Batallion Beach in Huntington, as they pointed to successes and challenges of improving water quality.

"The 2026 Long Island Sound report card gives us reason to be encouraged, but it also reminds us that our work is far from finished," Assemb. Keith Brown (R- Northport) said.

 "The good news is that the open waters of Long Island Sound continue to show meaningful improvement, which is a pattern that we love, and we should recognize why we are seeing that progress," he said. "Decades of investment in wastewater treatment and efforts to reduce nitrogen entering the sound are producing results."

The picture for bays that come off Long Island Sound proved different, with just more than half of the 62 measured registering an A or B in overall water quality, and 44% of bays from Connecticut to New York City, including Long Island's North Shore, receiving grades of C, D or F. 

Bays can receive poorer grades due to low oxygen levels or harmful algae blooms, officials said. Based on these factors, Huntington Harbor received a B while Northport Harbor was graded as a D. Middle Hempstead Harbor and inner Manhasset Bay received failing grades for similar reasons.

"Some of it's natural geography. They don't flush as well with the open waters of Long Island Sound. But some of the main stressors on our bays and harbors in respect to environmental health are fertilizer usage and stormwater runoff, a big vector of pollution to our bays and harbors," Linderoth said. 

Certain areas also received lower grades due to denser population and human activity on the water. Factors like converting to sewers instead of cesspools and reducing wastewater output have led to water improvements, Linderoth said.

Communities including Huntington and Oyster Bay have reseeded the bottom of bays with recycled oyster shells from restaurants and oyster seedlings to help restore the shellfish population.

Huntington worked with the Cornell Collective and Rotary International to spread 250,000 oysters along the bay last week and again on Tuesday, Huntington Supervisor Ed Smyth said. The town has also planted sugar kelp to improve water quality. 

The open waters of Long Island Sound north of Suffolk County saw improvement over the last biannual Save the Sound report, which was issued in 2024. These segments, referred to as the Eastern, Central and Western Basins, traditionally have had the best water quality. The Eastern and Central Basins registered A+ grades. The Western Basin scored an A.

The segment of the Sound north of Nassau County and a sliver of Western Suffolk including Huntington, dubbed the Eastern Narrows, registered the same grade of B as it did in 2024, but continued to show improvement when considered over the 18 years since the data being taken into account was first measured.

The westernmost segment of the Sound, the Western Narrows, remained the most impacted segment. But its grade improved from an F to a D for the first time since testing began in 2008, Linderoth said. 

The group based the grades on data from Connecticut and New York agencies and generated them by analyzing dissolved oxygen, chlorophyll a, water clarity and dissolved organic carbon water quality indicators.

Advocates credited Connecticut and New York wastewater treatment facilities for taking steps to reduce nitrogen from entering Long Island Sound.

"We're seeing this remarkable improvement ... largely based on wastewater infrastructure investments that are paying dividends," Linderoth said. "Those local actions are really key. So the grades help as a road map of identifying where we need to do some restoration and where we can do preservation."

Check back for updates on this developing story.

By John Asbury

john.asbury@newsday.comJohnAsbury

John Asbury is a breaking news and general assignment reporter. He has been with Newsday since 2014 and previously worked at The Press-Enterprise in Riverside, California.