Recent tests show that an intense, damaging brown tide has erupted in the Great South Bay and is spreading fast.

Stony Brook University's Dr. Chris Gobler says brown tide has rapidly intensified to more than 300,000 cells per milliliter in Patchogue Bay as of Wednesday -- the highest brown tide cell count on Long Island since 2017.

"Brown tide has been around for decades but when it shows up, they can kill off hard clams and that's one of the most important fisheries on Long Island," says Gobler. "It contributed to the collapse of that fishery in the '80s and continually, whenever it comes up, it's associated with the loss particularly if what we call early life stage clams. Those clams spawn now."

George Remmer, a fisherman for more than 50 years, says the bay used to be teeming with scallops, clams and fish. He says the resurgence of brown tide over the years has taken its toll.

"When I was a kid, we caught flounder in this canal," says Remmer. "I'd get in a 12-foot aluminum boat and catch half a bushel of flounder and my father said, 'You can't even use all the flounder you're catching.' I was just a little kid. Now, it's hard to catch one."

South Shore boat yard owner Bill Tunney says the brown tide is also raising concerns among boaters and people using personal watercrafts. He says he gets a lot of questions about why the water is brown.

Scientists say brown tide is caused by high nitrogen pollution, which can come from old cesspools and fertilizer runoff. Some solutions include avoiding fertilizer use and upgrading septic systems.

Scientists say brown tide is caused by high nitrogen pollution, which can come from old cesspools and fertilizer runoff. Some solutions include avoiding fertilizer use and upgrading septic systems.