Oxygen levels in the Long Island Sound are at their healthiest point in three decades, according to new research from the Long Island Sound Partnership.

It marks a major milestone after years of environmental decline.

The improvement is already helping marine life rebound, with more fish and other species returning to the body of water.

“You can think back 30 years ago, and you were not able to see any [dolphins or whales] in the Long Island Sound,” said Michael Martucci, the Environmental Protection Agency’s Region 2 administrator.

The findings come decades after a massive lobster die-off and years of hypoxia – low oxygen conditions that can lead to fish kills and the loss of marine ecosystems.

Martucci says better water quality has a direct impact on the Sound’s biodiversity.

“Better water quality brings more marine life to the area, more fish,” Martucci said.

The EPA says the progress is the result of decades of coordinated work, including reducing garbage, stormwater runoff and nitrogen pollution. Excess nitrogen can fuel harmful algae blooms that deplete oxygen in the water.

While the changes may not be obvious at a glance, higher oxygen levels are already creating healthier conditions for fish, shellfish and other marine life throughout the Sound.

The Long Island Sound Partnership says continued conservation efforts will be critical to maintaining the gains and ensuring oxygen levels, and marine life, continue to thrive in the years ahead.