Nutrient pollution—the excess of nitrogen and phosphorus in water—is one of the most widespread environmental challenges across the U.S. These nutrients fuel the rapid growth of algae, which can lead to oxygen depletion in the water, a process known as eutrophication. This harms marine life, damages ecosystems, and impacts industries like fishing and tourism.
Long Island Sound has long faced these issues, and its excess nutrient pollution was the impetus for the creation of the Long Island Sound Partnership and the development of the Total Maximum Daily Load (TMDL) plan by Connecticut and New York in 2000. The TMDL set enforceable limits on nitrogen entering the Sound to meet water quality standards and reduce hypoxia. Since then, nitrogen discharges from wastewater treatment plants have been reduced by 70%. Broader efforts—including stormwater management, agricultural best practices, and public engagement—have also helped cut pollution from diffuse sources across the watershed. These actions are already making a difference: summertime hypoxia in the Sound has been reduced by over 50%, exceeding targets set in the 2015 Comprehensive Conservation and Management Plan (CCMP).
Still, nutrient pollution remains a challenge. Algal blooms and seasonal hypoxia continue to occur. Warming waters may also require even greater nutrient reductions in the future to maintain current improvements.
The 2025 Comprehensive Conservation and Management Plan (CCMP) sets new goals to further reduce nutrient pollution and protect the health of Long Island Sound. The Partnership is advancing strategies to meet these goals as part of the ongoing TMDL framework.
To measure progress, the Partnership has outlined clear goals for both New York and Connecticut.
In New York, the focus is on implementing nine-element watershed-based plans in Suffolk and Nassau Counties. A key goal is reducing nitrogen from septic systems by upgrading or removing outdated onsite wastewater treatment systems and connecting more homes to public sewer lines. Progress is tracked by the number of systems replaced or improved.
In Connecticut, the Second-Generation Nitrogen Strategy is identifying nutrient reduction targets for six priority embayments. Success is measured by how many of these embayments have completed targets and by reductions in nitrogen loads from wastewater and rivers.
Across both states, additional indicators of success include:
Together, these efforts aim to reduce nutrient pollution and improve the overall health of Long Island Sound.
Learn more about the New York and Connecticut nitrogen reduction plans:
Nutrient Bioextraction combines growing and harvesting shellfish and seaweed for the purpose of removing nitrogen and other nutrients from coastal waters.
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Partners are building computer models and collecting data to simulate real-world land and water conditions.
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The Unified Water Study helps groups collect comparable data to monitor the health of Long Island Sound’s bays and harbors.
The EPA is implementing the Nitrogen Reduction Strategy to continue progress in reducing nitrogen as needed to achieve water quality standards throughout Long Island Sound, its embayments, and nearshore coastal waters.
Using agriculture best management practices such as planting cover crops, reducing fertilizer use, and managing animal waste helps reduce nitrogen runoff, protect soil, and support cleaner waters and healthier watersheds.
Learn how Connecticut and New York are working to reduce nitrogen pollution and improve water quality:
Hunts Point Wastewater Treatment Plant sludge pipe at west aeration tanks. Photo courtesy of NYCDEP
New York City has spent over $1 billion upgrading wastewater treatment plants to reduce nutrient pollution and improve water quality in New York waters, including Long Island Sound. Learn how they did it, and learn how the wastewater treatment process works:
View this chart for a visual explanation of how Hypoxia occurs. Download pdf
Late each summer, much of the water in Long Island Sound is trapped beneath a ‘pycnocline,’ the layer that divides lighter surface waters from the denser deep waters. Because it doesn’t mix with surface waters, this bottom water may have insufficient oxygen for fish, lobsters and other animals to live.
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