Billions of dollars invested in wastewater treatment and infrastructure improvements across Connecticut and New York appear to be producing results, according to a new report documenting continued gains in Long Island Sound’s water quality.
Save the Sound’s 2026 Long Island Sound Report Card found that water quality either improved or held steady in all five open-water regions of the Sound.
The Western, Central and Eastern basins each earned an A, while the Eastern Narrows received a B.
The most significant change occurred in the Western Narrows, which includes waters around New York City and improved to a D.
It was the first passing grade for the Western Narrows since Save the Sound began evaluating the region in 2008. Previously, the area had received an F every year.
The Western Basin rose from an A- to an A, and the Central Basin advanced from an A to an A+.
The Eastern Basin retained its A+ rating, while the Eastern Narrows remained at a B.
The report’s assessment of water quality is based on measures including dissolved oxygen, chlorophyll, water clarity, dissolved organic carbon and the balance of seaweed communities.
Researchers also track temperature, salinity, oxygen saturation and aquatic vegetation as part of the study.
Excess nitrogen can trigger algae blooms and create low-oxygen conditions that threaten or kill fish and other aquatic organisms.
Save the Sound said reductions in the amount of nitrogen entering Long Island Sound have played a major role in the improvements recorded in its open waters.
The organization launched its Unified Water Study in 2017 to develop a clearer picture of water quality in 52 bays and harbors throughout the Sound.
The program uses consistent monitoring methods, protocols and equipment, allowing data gathered by different organizations to be compared across the region.
Despite the positive findings, Save the Sound cautioned that climate change, warmer water temperatures and increasingly severe stormwater runoff could put the progress at risk.
The organization said continued reductions in nitrogen pollution, along with sustained investment in wastewater and stormwater infrastructure, will be essential to preserving the gains.
