Most of the toxic bunker fuel that leaked from a bulk carrier into Vancouver's English Bay has been cleaned up, officials say.

At a news conference on Saturday, assistant commissioner of the Canadian Coast Guard Roger Girouard said a Transport Canada flyover found only a "very thin veneer" of the black substance remained in the ocean, and that most of it "probably evaporated overnight."

He added that more than 80 per cent of oil from the spill has been recovered. It is estimated that 2,700 litres leaked into the bay from the Japanese-made ship MV Marathassa on Wednesday.

The focus of cleanup efforts are now being shifted to the picturesque shorelines near the city's downtown, the world-renowned Stanley Park and numerous popular beaches, Girouard said.

"On the shoreline, every indication that we have is that the soiling is in fact minor," he said.

"There are a couple spots where a one metre globule got on some rock and that will be addressed … but even on the worst impact site in West Vancouver, thankfully the impact is relatively minor," he added.

No marine mammals have been found in distress, and only three oil-soiled birds have been confirmed to be affected by the spill.

"The small number of impacted birds … is an indicator of how successful we were in getting the black oil out of the water as rapidly as possible," said Girouard.

Janelle VanderBeek, a co-ordinator at the Burnaby Wildlife Rescue Foundation of B.C., is helping tend to the sick birds.

"They are rather soiled," VanderBeek said.

"We are just triaging them for now, (and) doing our best with them.”

Girouard added that cleanup teams will continue to scour local beaches for the next few days, and into next week if necessary.

Officials say that they will focus on a 40-kilometre stretch of shoreline.

The source of the leak on the Marathassa has been "locked down," and Yvette Myers, the regional director of Marine Safety and Security at Transport Canada. Divers and marine safety inspectors have been out daily, she said, to ensure that no more oil is leaking from the vessel.

Divers have not inspected the bay to see if any bunker fuel has sunk to ocean floor.

However, Girouard said because of the characteristics of the oil and the speed of the response, he is "fairly confident" that it remained at the surface.

"(A) small amount of oil might accumulate around some flotsam, a piece of wood, or something weighted, it is certainly within the range of possibility, but we don't expect any significant volumes to have gone down to the ocean floor," Girouard said.

While the investigation into the cause of the leak is still ongoing, Girouard said that an "equipment malfunction" is likely to blame. The source has been pinpointed to a hull outlet.

Girouard called it a "great irony" that a new vessel that meets the latest standards, sustained a leak on its maiden voyage to collect grain in Vancouver.

He added that the owners of the ship have been co-operative and that they will be responsible for the cost of the incident under the Marine Liability Act.

Vessels in nearby ports will also be inspected to see if there is any buildup of oil on their hulls.

Girouard also advised locals who are keen on aiding the efforts to stay on the sidelines.

"There are still some soiled areas and it is bunker (oil), it is not healthy stuff, so … please don’t do any wildlife assistance on (your) own call us, let the professionals do the right thing … the animals will survive better without being stressed by well-meaning, but amateur activity," said Girouard.