The 25-metre Western Crusader capsized Tuesday morning, leaving an oily sheen stretching along the river.
No one was aboard the ship and there are no reports of injuries after the vessel overturned at the Shelter Island Marina in Richmond.
Michelle Imbeau, spokeswoman for Fisheries and Oceans Canada, says the slick left on the water is from engine or bilge oil and a boom has been deployed to catch the pollution.
Imbeau says the ship's fuel tanks were empty.
The owners have arranged for a crane to salvage the vessel. The Coast Guard is on the scene, monitoring the situation.
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