Long Island Sound Report Card Shows Improving Open-Water Quality

Monitoring the water on Long Island Sound. Photo/Save the Sound

LARCHMONT, New York/NEW HAVEN, Connecticut — September 22, 2026 – Regional nonprofit environmental organization Save the Sound has released its biennial 2026 Long Island Sound Report Card. Reflecting data from the 2025 monitoring season, nearly every section of the Sound’s open waters showed higher scores compared to the previous report. Conversely, separate grades for individual bays revealed continued localized environmental concerns.

Save the Sound tracks water quality across five segments of open water in the Long Island Sound, spanning from the East River to Fishers Island off the Connecticut coast. In this year’s report, every segment increased or maintained its grade compared to 2024:

♦ Western Narrows: Improved from F to D, demonstrating an improving trend and receiving a passing grade for the first time in 18 years of grading.

♦ Eastern Narrows: Received a B, demonstrating an improving trend and maintaining its B from the 2024 Report Card.

♦ Western Basin: Improved from A- to A, still variable over the 18-year trend.

♦ Central Basin: Improved from A to A+, remained stable over the 18-year trend.

♦ Eastern Basin: Received an A+, remained stable over the 18-year trend.

Save the Sound credits billions of dollars in wastewater treatment plant upgrades across Connecticut and New York for significantly reducing nitrogen levels. Open water data are gathered by the Connecticut Department of Energy and Environmental Protection, the Interstate Environmental Commission, and the New York City Department of Environmental Protection.

While nitrogen reductions have yielded open-water success, climate change risks—like rising temperatures and stormwater runoff—threaten to reverse these gains. Localized bays face steeper challenges. Only 56% of the 62 graded bay segments earned an A or B. Half received a C, D, or F for dissolved oxygen, which severely impacts marine life.

As with open water grades, it’s vital to be able to evaluate trends over time in the region’s bays, rather than focus on a single year of monitoring. In 2025, water quality data used for the Bay Grades were collected by 27 partner groups—including Save the Sound—through the Unified Water Study (UWS), now in its 10th season. Using eight years of UWS data (2018-2025), Save the Sound is now able to issue Bay Grade Trends, which evaluate performance over time, for all monitoring locations that have been part of the program from its first season.

The full report card is available at Save the Sound 2026 Report. An interactive map of current and historic grades is available at Sound Health Explorer, as are the new Bay Grade Trends.

Save the Sound leads environmental action in Connecticut, Westchester, NYC, and Long Island. They protect the Sound and its rivers, fight climate change, save endangered lands, and work with nature to restore ecosystems. Learn more at Save the Sound.

Written by Tom Schlichter

Illustration map courtesy of Save the Sound