Worst Brown Tide In Years Threatens Great South Bay

LONG ISLAND, NY —This year's brown tide in the Great South Bay is the worst since 2017, scientists at Stony Brook University say. The brown tide cell counts from the brown tide alga were found at high densities between Sayville and Bellport, at levels harmful to marine life, especially hard clams that reproduce in June.

Brown tides have been commonplace off the South Shore of Long Island since the mid-1980s, created by nitrogen runoff from lawns as well as septic tanks. The Peconic estuary once experienced similar harmful brown tides but has been free from them since 1995.

Christopher Gobler is the Chair of Coastal Ecology and Conservation in the School of Marine and Atmospheric Sciences at Stony Brook.

His monitoring found the brown tide had more than 300,000 cells per milliliter on June 23 in Patchogue Bay. Any density greater than 35,000 harms marine life, notably hard clams, scallops and eelgrass.

“The fate of these young-of-the-year clams may rest on the duration of the current brown tide which usually intensifies through June and into July until water temperatures get into the mid-70s.”

Gobler is hopeful that additional sewering on the South Shore will help the brown tides in the future.

“Great South Bay has the precise combination of conditions that leads to brown tides and other harmful algal blooms: Intense nitrogen loading from household septic systems into a shallow water body that is poorly flushed by the ocean,” he said.

“As efforts by Suffolk County move forward to address septic nitrogen loading, this region should improve as a result.”