More than 120 birds were killed at an oil sands mine operated by Suncor in Canada, the Alberta Energy Regulator (AER) said.
AER said the birds were found at the Fort Hills facility, 90kilometres north of Fort McMurray.
The birds are understood to have become caught in a pond of oil sands byproducts.
Fort Hills’ other co-owners include French energy giant Total and Canadian miner Teck Resources.
The regulator said: “We are working with Fort Hills Energy, the Government of Alberta, and the Government of Canada to ensure that all safety, wildlife, and environmental requirements are met during the response to the incident.”
A Suncor spokeswoman said: “We do have a full complement of bird-deterrent systems. We are engaging with wildlife experts in addition to the regulator to determine if there are additional measures that we can put in place.”