Suncor is dealing with a release of hydrocarbon at its Sarnia refinery.
The company said the release was identified Wednesday evening and crews responded immediately.
The source of the hydrocarbon release was identified and isolated.
As a precaution, response equipment including booms and vacuum units were deployed. Air monitoring is underway in the area.
"The safety of our people, community members and the environment remain our top priority," said Suncor in an notice from Sarnia-Lambton Alerts.
Suncor said all appropriate regulatory agencies and community organizations have been notified.
The incident is the second in less than a week at Suncor.
On March 27, Suncor reported a spill of crude oil to the St. Clair River, resulting in a do not use water advisory being issued by Lambton Public Health for private water intakes.
The clean up continues.