SAG HARBOR - The rust tide threat has returned to the East End, and officials say it could kill fish in the waters off the Hamptons.

Rust tide is named after an organism called cochlodinium that causes some of the waters to become a murky rust color.

Scientists say the rust tide is caused by nitrogen loading, which is caused by too many cesspools that don't work properly, too much fertilizer used on lawns and road runoff.

Dr. Christopher Gobler, who oversees the Stony Brook Marine Science Center in Southampton, says rust tide is different from green or brown tide seen in recent years on the East End. He says left unchecked, rust tide could kill Long Island's multibillion-dollar fishing and shellfishing industry.

"In the beginning of the summer, the scallop population of Peconic Bay looked very good," he says.  "And the rust tide came in, and the scallops sort of disappeared."