Cleanup crews are spreading booms around a fuel spill in an ecologically sensitive area off the northern coast of Vancouver Island that is frequented by orca whales.

On Monday, a barge operated by Ted Leroy Trucking spilled its load of heavy equipment and diesel fuel in Robson Bight, raising concerns about the impact on as many as 60 orcas, who gather in the area every day to rub their bellies on the gravel beach.

A Burrard Clean Operations vessel leaves Robson Bight on Tuesday.
(Terry Milewski/CBC)

Some have been seen swimming through an oil slick in the area that's estimated to be 14 kilometres long and up to 50 metres wide.

Burrard Clean Operations of Burnaby, B.C., has been hired by Ted Leroy Trucking and is on scene placing a protection boom around the areas that have been identified, said Jamie Toxopeus of the Canadian Coast Guard.

The trucking firm, based in Chemainus, B.C., will have to cover the cleanup costs.

It's not clear yet just how big a job the cleanup is going to be. Officials estimate 199 litres of fuel have leaked out so far, but as many as 10,000 litres of gasoline and diesel were on board the barge.

"Killer whales, as with other cetaceans, lack a sense of smell and so they would not be able to detect the presence of diesel through respiring in its vicinity and detecting it through smell," said John Ford, a whale researcher with the Federal Department of Fisheries and Oceans.

Crews started to work on cleaning up the spill on Tuesday.

Peter Ross, a marine mammal toxicologist with the Federal Institute of Ocean Sciences, said he's concerned the orcas might inhale the oil vapours, develop lesions on their lungs, get pneumonia or even die.

There's also concern about the residue that might be left on the beaches of Robson Bight as the light diesel fuel evaporates.