Last summer’s massive fish kill was caused by algal blooms, too much nitrogen, study confirms

A study released today confirmed that last summer’s massive fish kill in the Peconic River was caused by algal blooms.

Hundreds of thousands of bunker fish washed up dead in the Peconic river early last summer, leaving officials scrambling to clean up the rotting mess and determine the source of the kill.

A months-long collaborative effort between the state, the county and researchers at local universities determined that a spike in algal blooms, fueled by increased levels of nitrogen in the water, deprived the water of oxygen and caused “mass asphyxiation” in the river’s bunker.

A large population of predatory blue fish at the mouth of the river made matters worse, blocking the bunker from escaping the oxygen-drained river. The algal blooms also damaged the gills of the bunker, which are also known as menhaden, which may have exposed them to a virus.

The study discounted the possibility that illegal discharges, spills or the presence of toxic substances contributed to the kill.

Chris Gobler, a Stony Brook University research professor, identified algal blooms early on as the cause of the kill.

The spike in algal blooms were also the probable cause of a diamondback turtle die-off in the Peconic Estuary last May, according to Gobler. The study released today did not address the turtle kill, only the bunker.

High levels of nitrogen in the Peconic River are believed to have fueled the algal blooms. Residential septic systems, pesticides and fertilizers all contribute to increased levels of nitrogen.

The study estimates that roughly 300,000 bunker were killed in the Peconic Estuary last summer due to the nitrogen-fueled algal blooms. Most of the dead fish washed up at the mouth of the river, near Indian Island County Park and in the waters between the Route 105 bridge and the Riverhead Yacht Club, according to the study.

Officials on both the state and local levels have been working “aggressively” to reduce nitrogen loading into the Peconic Estuary and into waterways throughout Suffolk County.

Riverhead Town is currently undergoing major upgrades to its sewage treatment plant, funded partly by an $8 million grant from Suffolk County and $18 million in financing from New York State.

The state has also used $580,000 in grants from the Environmental Protection Fund to connect residential cesspools to Riverhead’s public wastewater treatment facility.

New York State Department of Environmental Conservation is also working with county and town officials to develop a Nitrogen Action Plan to reduce nitrogen throughout Long Island.

The DEC, the Suffolk County Department of Health Services and researchers at Stony Brook University and Cornell University all contributed to the study. They will continue monitoring the Peconic this summer for signs of another kill.

Anyone who sees evidence of a large fish kill should report it immediately to the DEC (631-444-0430) or to Suffolk County Department of Health Services (631-852-5750).