Shale sediment turned Mimico Creek green
Environment Ministry confirms cause of discoloration, says there’s no cause for concern
It took nearly a month for an Etobicoke man to find out that it was shale sediment that was turning the water in Mimico Creek a murky, grey-green colour.
“It’s great they’re finally getting to the bottom of it,” Craig Strathy said. “But it’s absolutely crazy it has taken this long.”
Ministry of the Environment, Conservation and Parks (MECP) spokesperson Gary Wheeler confirmed the cause Tuesday.
“We have confirmed the water in Mimico Creek was discoloured by mud from nearby construction,” Wheeler said in an email. “The shale/rock sediment in the mud can change the colour of the water from grey to green.”
Wheeler added that while the ministry takes all threats to the environment “very seriously,” it has no concerns at this time.
The ministry’s role is to respond to concerns, assess any environmental impacts caused by such incidents and ensure the appropriate and responsible agencies clean up the spill or site, Wheeler said.
Toronto Water initially took over responsibility for site cleanup, Wheeler said. However, the Ministry of Transportation (MTO) is working on the cleanup and monitoring of the area after it was determined to be an MTO outfall, Wheeler confirmed. In this case, the outfall is a concrete structure that drains water from the highway into the creek.
Lawson Oates, City of Toronto director of environment and administration, said Monday the city joined the MECP response by installing a containment boom, or temporary floating barrier, to block solid debris at the outfall, as well as straw bales covered in filter material.
Oates said two separate incidents in January contributed to the green discoloration in the creek; the first work on Jan. 3 related to Metrolinx construction, the second work on Jan. 15 related to an MTO contract. The work “involved some shale, which has a green sheen to it,” Oates said. “Some of that material is captured and some of it is carried on (in the water).”
It remains unclear what events may have led to shale being deposited in the creek and turning it green in December. Meanwhile, heavy rains about a week ago seem to have diluted the murky, grey-green colour of the creek in that area.
As for Strathy, he first noticed Mimico Creek’s strange colour over Christmas break during regular walks in West Deane Park with his dog. After Strathy noticed it a third time, he walked the creek trail from West Deane Park to identify the source of the discoloration.
MECP will continue to monitor the site to ensure the clean up is completed, Wheeler said.