The centre said 111 ducks were covered in oil after a truck overturned on a nearby highway and the mineral oil leaked into Mimico Creek on July 13. The driver was later charged with careless driving.
The Toronto Wildlife Centre's rescue team arrived at the creek the same day as the oil was discovered and began removing the ducks, transporting them to the centre where they were cleaned and able to recover.
They began returning the ducks to the creek on July 16, though some of the birds died from being exposed to the oil.
At around 11 a.m. Monday morning, Wildlife Centre volunteers unloaded the last six clean ducks from the transport van into the creek.
During the release, volunteers spotted one more sick duck, who was caught and will be transported to the Wildlife Centre for care.
The Wildlife Centre is urging people to make a donation to help recover the costs the Centre has incurred with this effort.