A key canal on the St. Lawrence Seaway has reopened three days after a leak spilled bunker fuel into the busy maritime lane south of Montreal.

A hole the size of a basketball found in the bulk carrier Richelieu's fuel tank was repaired on Thursday with the installation of a 10 metre-long steel plate "to seal the breach in the hull," said Canada Steamship Line, which owns the vessel.

Work crews are still mopping up diesel fuel that spread more than three kilometres along the shoreline after the Richelieu ran aground Monday night. It is not known how much fuel leaked from the ship.

The ship is moored at the Sainte-Catherine lock.

The spill delayed several other vessels waiting to pass through the canal. As of Thursday afternoon, 16 other freighters were lined up in the water.

The tie-up is costing the shipping industry about $150,000 a day, according to the St. Lawrence Seaway Management Corp.

Environmental damage has been minimal, "and it could have been worse," said Sonia Laforest, an Environment Canada spokeswoman.

About 12 birds were contaminated in the diesel spill, with half of them requiring veterinarian care at the University of Montreal.