Four hundred years ago, Dutch explorer Adrian Block was the first European to sail into Long Island Sound. He found a pristine body of water teeming with aquatic life. That, sadly, is not the Sound we know today. But the good news, after decades of degradation, is that progress finally is being made to clean Long Island Sound.

Governments in New York and Connecticut deserve credit for following through on a plan developed with the U.S. Environmental Protection Agency in 1998 to reduce nitrogen pollution in the Sound by 58.5 percent. An environmental watchdog group this week gave Nassau and Suffolk counties grades of A for completing virtually all upgrades to the 10 sewage treatment plants that discharge into the Sound. Connecticut also received an A, while New York City and Westchester County, which have finished some upgrades but still have significant work ahead, were given B's.

advertisement | advertise on newsday

High levels of nitrogen lead to summer "dead zones" in the western Sound, when the huge algae blooms that thrive on nitrogen die off, settle to the bottom and deplete oxygen levels as they decay. The lack of oxygen kills marine life or causes it to flee, contributing to the virtual disappearance of many species, most notably lobsters. Another problem has arisen: Climate change has increased the water temperature slightly, which also reduces oxygen. That makes nitrogen removal all the more important, and though it's early in the recovery process, environmentalists say the dead zones seem to be shrinking. Officials must continue to monitor the sewage plants to make sure they meet their targets.

We might never return Long Island Sound to what Block found in 1614, but progress over the last 15 years creates hope that it can once again become vibrant.