2025 CEQ Annual Report

Water

Rivers, Lakes, and Estuaries                Warming and Rising Waters               Swimming              Clamming and Oystering                Drinking Water

The Water of Long Island Sound 

The maximum area of Long Island Sound with hypoxia, which is water with a dissolved oxygen (DO) concentration less  than 3.0 milligrams per liter (mg/l), decreased from 43.4 square miles in 2024 to 18.3 square miles in 2025; a decline of approximately  58 percent from the previous year and an 80 percent decline from the previous ten year average. The duration of the hypoxic conditions increased from 38 days in 2024 to 40 days in 2025.³⁵  Several factors, such as the state’s Nitrogen Control Program, improvements to wastewater treatment facilities, and better controls for stormwater runoff have significantly reduced the area of hypoxic conditions in Long Island Sound since pre-2000 levels. 

Goal: The goal line on the top chart approximates the maximum area (~150 miles²) of the hypoxia target to "measurably reduce the area of hypoxia in Long Island Sound … by 2035”.³⁶

Nitrogen Discharges

In 2025, the annual average aggregate equivalent nitrogen load (pounds per day) discharged from the publicly owned treatment works (POTW) in the state to Long Island Sound (6,331) decreased by approximately 22 percent from last year (8,133) and 20 percent from the previous ten-year average (7,917).³⁷

The decrease in nitrogen discharges in 2025 was due, in part, to improvements in the POTW facilities, and warmer and dryer weather. Nitrogen discharges from states “upstream” of Connecticut can contribute to nitrogen loading of Connecticut’s rivers and the Long Island Sound.

Goal: The total maximum daily load (TMDL) nitrogen reduction goal is based on a 63.5 percent reduction from the baseline load of 25,100 equivalent pounds per day (9,162) by 2014.³⁸

_{—————}

³⁵ _{DEEP; Long Island Sound Water Quality and Hypoxia Monitoring Program, personal communication from K. O’Brien-Clayton, November 10, 2025; 2025 Hypoxia Season Quick Facts; portal.ct.gov/DEEP/Water/LIS-Monitoring/LIS-Water-Quality-Monitoring-Maps.}
³⁶   _{Long Island Sound Study, Comprehensive Conservation and Management Plan, 2015; longislandsoundstudy.net/2015/09/2015-comprehensive-conservation-and-management-plan/.}

³⁷ _{DEEP, Nitrogen Control Program for Long Island Sound; personal communications from I. Raffa, April 15 and 22, 2026.}

³⁸ _{DEEP, Nitrogen Control Program for Long Island Sound; portal.ct.gov/DEEP/Municipal-Wastewater/Nitrogen-Control-Program-for-Long-Island-Sound.}