"We continue to do some monitoring and will base our decisions for actions on the data collected," Bartos said. "But I don't think there will ever be a removal again in the river. I think it has been adequately removed."

Headquartered in Charlotte, Duke is the nation's largest electricity company. In past statements to investors, executives have said they do not expect costs incurred from the cleanup effort to be large enough to affect the $50 billion company's profitability.

Duke spokesman Jeff Brooks stressed Thursday that even though the cleanup effort is complete, the company is still in the early stages of developing a study with the U.S. Fish and Wildlife Service to track the long-term impact of the spill on aquatic life.

"This is just one aspect of our response," Brooks said. "We're not going away from the Dan River, and we continue to be committed to the communities along the Dan River. We'll be there for the future, and we'll work to keep the Dan River moving forward and remaining healthy."