US Coast Guard crews spent the weekend investigating a possible leak from a sunken barge near Kelly's Island, Ohio, south of Pelee Island.
Diving enthusiasts noticed an unknown substance and a smell of solvent leaking from a barge that sank during a storm in 1937.
Coast guard officials setup a 365 metre zone around the possible leak.
A helicopter flew over the zone Saturday and saw a discolouration in the water, but none was noticed during a similar fly over yesterday.
Salvage crews will be on scene Tuesday to secure the leak. Meanwhile, coast guard teams will continue fly overs to ensure the substance isn't spreading.
