Michael Risinit

Several Westchester County sewage treatment plants discharge into Long Island Sound.

Save the Sound gave Westchester a "B" for nor removing enough nitrogen from their treated discharges.

Too much nitrogen in the Sound leads to less oxygen, which harms fish and wildife.

Westchester says it will meet the requirement by the 2017 deadline.

Westchester County may be doing good work when it comes to improving Long Island Sound's water quality but needs to be doing even more to rise to the top of the class, according to an advocacy group watching over the Sound.

Connecticut-based Save the Sound gives the county a "B" on a report card issued Monday. The group found the county's sewage treatment plants discharging into the Sound are not removing as much nitrogen as they should.

High levels of nitrogen in the water body fuel too much algae growth. When the algae dies and begins to rot, it sucks oxygen out of the water. The lack of oxygen often creates a summertime dead zone in the Sound off Westchester, harming fish and other wildlife.

"If we can restore oxygen to the Sound, what our best scientists say is we're going to see a percentage increase in life in the Sound," said Curt Johnson, executive director of Save the Sound, which plans to open an office this spring in Mamaroneck.

Westchester's good but not perfect grade is because its plants are not reducing nitrogen pollution in their treated discharges by 58.5 percent, a figure Connecticut, New York and the federal government agreed to 15 years ago in order to restore the Sound.

"The report card is very positive. They've (Westchester) done a lot but they are an at-risk student," Johnson said.

By 2017, the county's plants in Port Chester, Rye, Mamaroneck and New Rochelle on average must meet that reduction level. Results from an upgrade at the Mamaroneck plant will fully kick in this year and similar construction at New Rochelle's plant is almost done, said Westchester's Environmental Facilities Commissioner, Tom Lauro.

Small modifications at the Rye plant are also coming, he said.

"We're headed toward a completion date and expect to meet it," Lauro said.

Connecticut received an "A" for its sewage plants already meeting the requirement. New York City was also given a "B."

Map: Locations of impacted sewage plants