Duke Energy was fined $102 million last week for polluting four major rivers with toxic coal ash over a number of years.

The electricity company pleaded guilty on Thursday to nine criminal violations of the federal Clean Water Act for discharging coal ash from five power plants in North Carolina, and for failing to properly maintain equipment at the facilities, the Los Angeles Times reported.

Four of the nine violations were related to an incident in February 2014 in which up to 39,000 tons of coal ash and millions of gallons of coal-ash wastewater were released into the Dan River. The thick sludge was carried 70 miles along the river to the Virginia border.

Duke Energy will pay $68.2 million in fines and spend a further $34 million on environmental projects that will benefit rivers and wetlands in North Carolina and Virginia. The utility said that this money will come from shareholders, not customers.

U.S. District Judge Malcolm J. Howard, who approved the plea deal, noted that it was the largest federal criminal fine ever imposed in North Carolina.

Commenting after the case was concluded, Assistant Attorney General John C. Cruden of the Justice Department's Environment and Natural Resources Division said: "The massive coal ash spill into North Carolina's Dan River last year was a crime and it was the result of repeated failures by Duke Energy's subsidiaries to exercise controls over coal ash facilities.

"The terms of these three plea agreements will help prevent this kind of environmental disaster from reoccurring in North Carolina and throughout the United States by requiring Duke subsidiaries to follow a rigorous and independently verifiable program to ensure they comply with the law."

Duke Energy was also sentenced to five years' probation. During this period, the company will be monitored for compliance and could face further court action if it violates the Clean Water Act.