Officials would like to trace the source of what is believed to be a diesel spill at the mouth of False Creek, but say the fuel was already dissipating even as they began investigating last night.

An oily sheen was spotted on the water under the Burrard Street Bridge yesterday evening, prompting a coast guard response.

It's unclear how much fuel was leaked or where it came from.

A tweet from the city says the coast guard continues to monitor the situation but the fuel was already breaking up and evaporating on its own, within hours of the first report.