PHILADELPHIA (AP) -- Authorities say they still don't know why there's an oil sheen on the Schuylkill River in Philadelphia.
U.S. Coast Guard Duty Officer Thomas Peck tells The Philadelphia Inquirer investigators with the Coast Guard and the city Fire Department plan to return to the river Tuesday morning.
Peck says the sheen, which was first reported to police around 5 p.m. Monday, could be runoff from cars.
Investigators had left the area Monday around 8:30 p.m.
Peck says the sheen seems watered down and doesn't appear to be dangerous.