Crews have been out since Sunday night cleaning up the diesel spill caused by a ruptured underground tank.

A construction crew at Vanderhoof and Brentcliffe, near Eglinton, apparently pierced a 10,000-litre underground tank, allowing diesel to seep into the sewage system.

The diesel entered the river through a sewer at Leslie and Eglinton.

Cyclist Kevin Kelly was reportedly the first one to spot the problem in the water.

"I noticed just a toxic odour in the air. It was like very overwhelming, like diesel fuel or something like that and I observed the river and it was just orange," he said.

The mess has since been contained by sand at the spill site. Crews are sucking the diesel out of the water.

It still isn’t known why the tank was there. Authorities said the spill is considered low-grade and doesn’t pose a danger.