The cause for the oil seepage into Burrard Inlet that had resulted in a small marina-like sheen on the water has yet not been traced by Chevron Canada.

Chevron Canada was wrong not to warn the city earlier of the oil seepage, that crews are now trying to contain in the Burrard Inlet, the mayor of Burnaby says.

Derek Corrigan seeks an explanation, as to why the company remained silent for three weeks after finding a mixture of gasoline, diesel, crude oil and water in a ditch near their refinery in Burnaby Heights, as well as an oily sheen on a 25-metre-wide section of nearby beach.

"They [Chevron] believed it was minor. We said, 'Well, exactly the opposite”, Corrigan told The Province”. “Obviously, anytime there's any kind of seepage that beats their containment system... we're concerned”.

The crews have been trying to enclose the seepage and spot its source, Chevron spokesman Ray Lord said on Thursday.

Crews are collecting any oil mixture they find at the original ditch, cleaning up the beach and monitoring samples taken from area wells to prevent any more of it from seeping into the inlet, he said.

The public and wildlife are however, not threatened.

Corrigan said Chevron detected the seepage on April 21, and notified the city on May 13, but he should have been more open about the incident to avoid further trouble.

Lord couldn't say how long oil has been leaking, or how much had been leaked because most of it is found in water.

However, B. C.'s Ministry of Environment, which will continue to supervise Chevron's containment efforts, said in a statement, it is about 50 liters of hydrocarbons, and "significantly small”.