Fire crews are investigating a chemical spill in the Humber River in Toronto’s west end.

More than 40 firefighters were called to the scene near Albion and Weston roads around 7 p.m. Saturday evening after a man passing by the river spotted a slick on the water.

Fire crews traced the substance to a storm drain near Islington Road.

Toronto Fire Service district chief John Zovak told CP24 that crews were able to isolate the spill, and that the substance appeared to dissipate in the water.

Zovak said crews were working to identify the substance and its origin.

“We believe it’s a polar solvent that was dumped into one of the storm drains in the city,” he said.

The Ministry of Environment has also been called to the scene to investigate.