Photo by Kimberly Panian

About 20 Canada geese are back in their natural habitat, following an oil spill in the Potomac River last month. After being rescued and cleaned, they were released back into the water today, the Washington Post reported.

During the contamination’s investigation, Delaware-based Tri-State Bird Rescue and Research group took 60 waterfowl out of the Roaches Run Waterfowl Sanctuary (which feeds into the Potomac), and 29 of those birds have died, according to the Coast Guard, The Post reported. On Friday, a duck was put back in the river, the rescue group said, and ten more geese are still undergoing treatment.

A few days after the oil sheen was spotted, the first batch of geese was found covered in oil and sent to be treated by the wildlife experts. Coast Guard officials also began monitoring the waters, deploying cleanup crews, and using oil-removal methods while searching for the source.

On February 12, Dominion Virginia Power said in a statement that a 13,500-gallon spill of mineral oil at its Crystal City substation was the cause. Now, the utility company could face financial penalties and reimbursement costs, following a violation notice that was sent from the Virginia Department of Environmental Quality last week.

The Coast Guard reported no additional sheening in the river and no additional harm to wildlife as of last week.