Officials from Port Metro Vancouver continue to investigate the source of a mysterious black sludge that washed ashore Friday afternoon.

The oily-looking substance washed onto Sunset Beach, located west of downtown Vancouver, around 4 p.m. Swimmers have since been advised to stay out of the water.

"We were literally about to go in there, just before they stopped us,” one beach-goer told CTV Vancouver. “Thank goodness they stopped us."

A port spokesperson said the substance is not oil, but rather ash or soot.

The port authority and the Canadian Coast Guard continued working together on Saturday to determine how to clean up the spill.

Port harbour patrol boarded deep sea vessels in the area on Friday night, but determined they were not the source of the sludge.

City of Vancouver Park Board Commissioner Constance Barnes said the substance is believed to be a carbon deposit that likely came from a recreational boat.

Barnes urged the boat’s owner to come forward so officials have a better idea as to how to treat the spill.

"As tough as it might be, pick up the phone and let us know. Because then what happens, it gives us an opportunity to know if it's a chemical, to know if it's oil, to know how to treat it."

She said the substance isn’t believed to be toxic.

Resources from the Kitsilano Coast Guard Station were deployed to the contaminated area immediately after the spill was reported, according to Barnes. However, she is worried that plans to close the federally-funded station next spring will hamper future clean-up efforts.

“These are the people who are first responders. This is an establishment that we desperately need,” said Barnes. “We are hoping to really keep the fight up to make sure they are here.”

In May Ottawa announced it would be closing the Vancouver coast guard station and city officials have since been urging the government to reverse its decision.

With a report from CTV Vancouver’s Nafeesa Karim