For a second straight summer, the Long Island Sound was far healthier than a decade ago, with fewer oxygen-deprived dead zones, according to the U.S. Environmental Protection Agency.
An EPA report released Thursday found that oxygen-depleted waters that can suffocate marine life were only slightly larger in size than last year, when the dead zones were the smallest since 1997.
Conditions improved because the weather was favorable and most of New York's wastewater treatment plants and all of Connecticut's were upgraded to strip out harmful nitrogen, said Mark Tedesco, EPA's Long Island Sound office director.
"The good news is there is a lot of progress," Tedesco said.
As nitrogen levels in waters gradually decline, levels of dissolved oxygen that fish and shellfish need to thrive should rise. "We expect that the water quality will lag the pollution reduction," he said.
Tedesco said treatment facilities in New York City and Westchester that haven't yet complied with the new standards are required to do so by 2017.
Every summer, excess nitrogen caused by storm runoff from gardens and fields, and flooded cesspools and septic systems, spur algae blooms where oxygen-consuming bacteria thrive. This kills shellfish, drives out fish, crabs and lobsters, and forces beaches and fishing grounds to close to protect people from pathogens.
Last summer, the Sound had 87 square miles of dead zones, six more than in 2013, according to the EPA. In 2012, the problem area spanned 289 square miles -- "one of the most severe on record," the agency said.
Chris Clapp, a marine scientist with The Nature Conservancy in East Hampton, said additional measures are needed, such as assessing watersheds to identify the biggest polluters.
"The silver lining should be that we address the nitrogen coming from all sources, not just the sewage treatment plants," he said.
Almost all of Nassau has sewers, although some North Shore communities do not, Clapp said.
But about 70 percent of Suffolk homes lack sewers and fixing that problem is a top priority for County Executive Steve Bellone.Bellone expects to announce next week which companies have been chosen to demonstrate how their treatment systems perform for individual residences or for neighborhoods, a spokesman said.
The pilot program should launch by the end of this year.