RIVERHEAD - Marine biologists say mahogany tide is to blame for thousands of dead fish that washed up on shore on Long Island's East End over the weekend.

Mahogany tide is a type of algae that promotes low oxygen levels in the water.

Experts say the mahogany tide is produced by increased levels of nitrogen, which stems from human waste, fertilizers and the sewage treatment plant in Riverhead.

Riverhead Town Supervisor Sean Walter says the town does not have enough resources to get rid of all the dead fish and that "nature is probably going to have to run its course."

The Department of Environmental Conservation has not yet returned a call to comment about the washed up fish.