A mysterious white fluid spotted bubbling up in Vancouver's Coal Harbour Saturday morning may be waste associated with construction activity, city officials say.

Residents walking along the waterfront noticed the whitish-grey flow bubbling up from below sometime around mid-morning.

It took some time, however, to sort out what the substance may have been.

First responders were baffled.

"At this time we don't know what the substance is," said Vancouver Fire and Rescue Services Battalion Chief Rod MacDonald, whose crew arrived at the scene at around 11 a.m. PT.

MacDonald said it appeared the milky liquid was coming from an underwater storm water outflow pipe.

"We're waiting for the arrival of [the] sewers [department] so they can indicate to us whether this is a normal situation or not," he said.

49.293740, -123.132050Location of Coal Harbour flow

At 1:30 p.m., an agent from the City of Vancouver's environmental protection branch arrived on scene.

Shortly after 2 p.m., workers from the city's sewer department arrived.

They confirmed the discharge came from a storm sewer and, whatever it was, the flow had stopped by mid-afternoon Saturday.

Sewer operations workers flushed the pipe with clean water and said no more of the strange fluid was coming out.

They suspected materials from a construction site may have been dumped into a street-side storm water collection grate somewhere in Coal Harbour or the West End.

City officials say that kind of dumping is against city by-laws, but has happened before.

MacDonald said agencies with the Port and with the federal government were notified about the incident, and that no dead fish have been spotted yet in the area of the outflow.

"The wildlife in the area seem to be OK so far," MacDonald said. 

"It's a positive sign, but not a conclusive sign."

With files from the CBC's Chad Pawson