Crews in Saskatoon were continuing to clean up an oily spill on the South Saskatchewan River Friday morning.

On Thursday, a passerby called the city after spotting a glob of oily material on a sandbar along Spadina Crescent on the west riverbank.

Upstream, it turned out a substance was leaking out of a storm drain near 33rd Street and Spadina Crescent, the Saskatoon fire department said.

The material appears to be not oil but some kind of road sealant that doesn't dissolve in water, said Brenda Wallace, the city's manager of environmental services.

Some of the material floated downstream, but some ended up at the bottom of the river, she said.

"It's a heavier, denser material. Some of it does sink," she explained.

A cleanup was underway throughout the night and continued in the morning.

Crews used booms to contain the spill and were planning to install a mesh on the outflow pipe to screen out the blobs and solid chunks.

What's not known yet is how much of the material ended up in the river, where it was put into the storm sewer and who put it there, she said.

The city will be working Friday to find out who's responsible.

mi-spill-vehicle-120615

Saskatoon fire department trucks were at the scene of an oil spill on Thursday night. (Courtesy Jay Kennard)