FORT MCMURRAY, Alta. -- Syncrude has agreed to plead guilty and pay $2.75 million in fines over the deaths of 31 great blue herons at an Alberta oilsands mine.

The birds were found dead or dying in 2015 at an abandoned sump pond at Syncrude's Mildred Lake mine north of Fort McMurray.

Syncrude subsequently faced charges of failing to properly store a hazardous substance under Alberta legislation as well as federal charges under the Migratory Birds Act.

The company says in a release that bird deterrents used on tailings ponds weren't in place for smaller bodies of water.

It says those ponds are now included in its waterfowl protection plan.

In 2010, Syncrude was fined $3 million after more than 1,600 ducks died when they landed on a tailings pond.

That same year, more than 550 birds had to be killed when an early winter storm forced them to land on waste ponds belonging to Syncrude and Suncor Energy.