Just when it appeared that despite unusual summer heat, waters around Shelter Island remained algae free, there have been sightings by neighbors around West Neck Harbor of what they thought was brown tide.

Not the case, according to a spokeswoman for the Suffolk County Department of Health that monitors brown tides and their possible effect on shellfish in local waters. But there have been hints of red tide, another toxic algae that endangers marine life, according to Dr. Christopher Gobler of Stony Brook University’s Southampton School of Marine and Atmospheric Sciences.

On August 1, tests revealed no brown or red tide, according to Health Department spokeswoman Julie Nathan. The tests were repeated on August 23, still with no signs of red or brown tide, but by September 1, there were some streaks of red tide in both Shelter Island and Greenport waters, according to Dr. Gobler.

Red tide is caused by the dinoflagellate, cochlodinium, according to Dr. Gobler. It’s not a threat to humans, but affects marine life, he said. Fish exposed to dense cochlodinium blooms don’t generally survive more than six hours.

Algae blooms become more severe because of nitrogen flows into the bays from cesspools and fertilizer, Dr. Gobler said.

That’s why the New York State Department of Environmental Conservation had continued to tighten regulations affecting nitrogen output from local sewer systems operated by the Heights Property Owners Corporation and the Greenport municipal system, he said.

On the hopeful side, Dr. Gobler said a $3 million grant from the Laurie Landeau Foundation is enabling him and fellow scientists to engage in an environmental restoration project in Shinnecock Bay that if successful, could lay the groundwork for restoring the ecosystems in other waterways.