Damaging brown tide has returned to the Great South Bay for the sixth year.

This year's harmful algae bloom has been spotted even earlier than in past seasons.

Dr. Chris Gobler, a Stony Brook University professor, studies harmful algae blooms and says the brown tide, which first appeared in the mid-1980s, is only getting worse.

"Brown tide is toxic to shellfish," he explains. "It's responsible for the collapse of the scallop industry on Long Island and contributed to the decline in clam landings since 1985."

Environmentalists say the root of the problem lies not in the bay but on the mainland. Gobler says failing cesspools and fertilized lawns are creating a nitrogen-rich toxic cocktail in Long Island bays, which is perfect for algae blooms. He adds that water flowing through the channel created by Superstorm Sandy is helping bays east of the channel, but "the center part of the bay is more stagnant and is more hospitable for brown tide."

Marshall Brown, head of environmental nonprofit Save the Great South Bay, says nothing has changed to make a dent in nitrogen loading along the shores. His group is focusing efforts on native plantings on the mainland that absorb nitrogen and will ideally clean water before it reaches the bay.

"The bay is a symptom of the mainland, which is sick," Brown says.

Brown and other environmentalists are planning to meet for a roundtable discussion in July to discuss ways to combat the brown tide and take serious action when it comes to Long Island's water quality.