Residents who share a backyard with a Babylon canal say its waters have turned black.

Multiple agencies, including the Department of Environmental Conservation and the Coast Guard are investigating the murky waters in the canal on Little Neck East Road and South Bay Drive.

People in the area told News 12 Long Island say there is a very strong smell seeping into their homes.

Resident Patricia Hultz said she has lived on the canal for 50 years and has never seen anything like it.

"We just don't know what it is and now we've had incidents where the swans are turning black on their feathers… Down the street, we've had horseshoe crabs, they're dead. And we don't usually see those. Something is happening," she said.

Investigators have put an oil absorbent boom in the canal.

The Coast Guard determined that the black substance is not oil or gas. The county will be testing sometime before Wednesday to determine what the mystery black water is.

The county also ruled out black and brown tides.