Long Island Sound's water quality improves; Western Narrows passes since 2008

Save the Sound released its 2026 Long Island Sound Report Card, showing that water quality improved or remained stable across all five open-water regions of the Sound. The biennial report, based on 2025 monitoring data and detailed on Save the Sound's own Report Card project page, grades the open Sound using four water quality indicators and 62 bay segments across 46 bays and harbours using five.

The standout finding indicated the historically worst-performing region, the Western Narrows near New York City. They posted their first passing grade in nearly two decades. Here's how each region fared, and what's driving the improvement.

Western Narrows earns its first passing grade since 2008

The Western Narrows, which includes the waters around New York City, received a D grade in the 2026 report, Fox Weather reports, marking the biggest improvement of any region and the first time it has received a passing grade since Save the Sound began grading the area in 2008.

Every prior year, the Western Narrows had received an F. Save the Sound's own project page notes the organisation has long identified high nitrogen and nutrient levels as the biggest overall problem affecting the Sound's health, contributing to dead zones, algae blooms and marsh damage, particularly in this densely populated western stretch of the estuary.

How the other open-water regions of the Sound fared

Beyond the Western Narrows, every other open-water region either improved or held steady.

According to CT Mirror, the Western Basin improved from an A- to an A, and the Central Basin improved from an A to an A+. The Eastern Basin maintained its A+ grade, while the Eastern Narrows remained at a B. Altogether, the Western, Central and Eastern basins all received A grades in 2026. These open-water grades are based on four indicators, dissolved oxygen, chlorophyll a, water clarity, and dissolved organic carbon.

Meanwhile the bay grades draw on five indicators, including dissolved oxygen, chlorophyll a, water clarity, temperature, and the presence of seaweed.

What's behind Long Island Sound's continued improvement

Save the Sound attributed the gains largely to billions of dollars in wastewater and infrastructure upgrades across Connecticut and New York, alongside continued reductions in the nitrogen entering the Sound. Excess nitrogen fuels algae blooms and contributes to low-oxygen conditions that can harm or kill fish and other aquatic life, so cutting nitrogen inputs has remained a central focus of the region's water quality efforts.

Save the Sound's Unified Water Study has supported this work by establishing standardised monitoring procedures, protocols and equipment across 62 of the Sound's bays and harbours, allowing data collected by different organisations to be reliably compared region-wide.

Why Save the Sound warns the gains remain fragile

Despite the improving picture, Save the Sound via Fox Weather cautioned that this progress could still be undone. The organisation pointed to climate change, rising water temperatures and worsening stormwater runoff as ongoing threats to the Sound's recovery. Save the Sound said continued reductions in nitrogen pollution, along with sustained investment in wastewater and stormwater infrastructure, will be essential to maintaining the results achieved so far.