Experts will try to determine what caused the death of a 25-foot whale, whose carcass was discovered washed up on a Fire Island beach Monday, Suffolk County police said.

Police said the whale carcass was found by a passerby in the surf line at Ocean Ridge, just east of Davis Park, at about 8:30 p.m. The passerby called 911 to report the find.

Marine Bureau officers responded to the scene and then notified the DEC and the Riverhead Foundation, police said.

The type of whale was not immediately known.

The cause of death is pending a necropsy.