SOURCE:
https://www.newsday.com/long-island/environment/long-island-sound-dead-zones-bvoi7i5g
By Tracy Tullis - December 8, 2025
Low-oxygen areas in Long Island Sound dropped last summer to the smallest footprint recorded in nearly 40 years, according to data from Connecticut’s Department of Energy and Environmental Protection.
"This is great news," said Adrienne Esposito, executive director of Citizens Campaign for the Environment in Farmingdale. "This is what happens when you have reliable funding, meaningful collaboration, strong public support, and good science — all working together."
The Connecticut agency monitors dissolved oxygen levels at 48 stations in the Sound through the summer months, including in Long Island bays and along North Shore beaches.
Hypoxic zones in the Sound extended to 18.34 square miles, the largest area for the year, for three days in July, DEEP found.
That was the smallest hypoxic area recorded since 1987, when the DEEP and other participants in the Long Island Sound Study, now the Long Island Sound Partnership, started collecting data.
The hypoxia zones last summer were slightly smaller than the Partnership’s forecasting model predicted and arrived slightly earlier, but was within the expected range, the Partnership said.
Low-oxygen zones, also known as "dead zones," develop in warm, nutrient-rich waters, which encourage the runaway growth of algae. When that biomass dies, it sinks to the ocean floor and decomposes, consuming oxygen. Low levels of dissolved oxygen inhibits the growth of clams, oysters and scallops, Chris Gobler, a professor of coastal ecology at Stony Brook University, found. If oxygen levels fall very low, fish, crustaceans and shellfish can't live in those water and may suffocate and die in large numbers.
For years Long Island’s waters have been plagued by low oxygen or hypoxic zones, especially in near-shore bays and inlets, where water warms faster and excess nutrients from lawn fertilizers, stormwater runoff, wastewater treatment plants and older septic systems flow into the water.
Esposito attributed improvements this year to a number of long-running efforts to reduce nitrogen pollution in the Sound, including wetlands restoration, upgraded septic systems, and stormwater filtration projects. "But the main factor," she said, "is the upgrading of the sewer treatment plants to include the denitrification technology."
"It really has been a massive effort for the last two decades," she said. She expects nitrogen levels and hypoxic zones will continue to drop as these projects continue and expand.
Researchers at the University of Connecticut note that continued progress will be necessary to keep up with a warming planet. Even if the amount of nitrogen in the Sound stays at present levels, warming oceans will encourage more algal growth, and deplete oxygen levels, since warm water can't hold as much dissolved gasses as cold.