The source, composition and quantity of the toxic fuel that spilled out into the waters of English Bay in Vancouver Wednesday afternoon is still unconfirmed.

In a news conference Thursday afternoon, Roger Girouard, head of the Canadian Coast Guard western region, said that the spill was being treated as either bunker fuel or raw crude in a "worst-case scenario" until test results came back.

Residents were being warned to avoid the beaches on both sides of the bay on one of the sunniest days of the year, and to keep their dogs leashed and away from wet sand as a cleanup operation continues.

Girouard said that two large patches of the spill had been spotted moving towardthe North Shore of the city, and had been collected immediately.No large slicks had touched the shoreline, he said, but there was "sheen material and some black tar balls" on the beach.

Fourteen hundred litres of the spill had so far been collected, he said, with a rough assessment of a total 2,800 litres present in the water.

The spill occurred in Vancouver's picturesque English Bay. (CBC)

That amount was "above the norm" but not "catastrophic."

The source of the spill remains unconfirmed, as crew ofthe grain ship Marathassa, which sat in the middle of the spill, denies they released any material, Girouard said, noting that lawyers are involved.

"We can't definitively say it came from that vessel," he said. "The master says they are not the source of the oil."

Girouardsaid that from an operations perspective, the response had gone "according to doctrine,"but he acknowledged that communications to the City of Vancouverandits residents "could have been better."

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Toxic fuel from English Bay spill washes up on Vancouver beaches