A dam breach at a retired North Carolina coal-fired power plant Friday may have allowed coal ash to flow into the Cape Fear River, Duke Energy officials said.

Floodwaters from Hurricane Florence continued to overtop an earthen dike at the north side of Sutton Lake, the 1,000-acre reservoir at the L.V. Power Station near Wilmington, Duke Energy spokeswoman Paige Sheehan told The Associated Press.

The water caused breaches in the dam on the south end of the lake, which is flowing back into the river. Sheehan said floodwaters had also overtopped a steel retaining wall containing one of three large coal ash dumps lining the shoreline.

Duke Energy couldn’t rule out that ash might be escaping and flowing into the river, Sheehan said. Coal ash contains arsenic, mercury and other toxic metals.

Gray material the company characterized as lightweight coal combustion byproducts could be seen floating to the top of the lake, which is now used for fishing and boating.

State regulators had been notified that the L.V. Sutton Power Station was at the highest alert level under Duke Energy’s emergency action plan.

According to The Associated Press, the plan defines an Emergency Level 1 event as: “Urgent! Dam Failure is imminent or in progress.”

“Flash flooding will occur downstream of the dam,” the manual reportedly says. “This situation is also applicable when flow through the earth spillway is causing downstream flooding of people and roads.”

The language is characterized as a “worst case scenario to allow everyone to prepare accordingly,” Sheehan said Thursday.

She said the company has been in contact with local emergency officials but high water levels meant “if the berm were to break, there would be very minimal impact down river.”

The lake is a former cooling pond for the Sutton power plant and is adjacent to three large coal-ash dumps. The power plant was retired in 203 and replaced with a natural gas powered-generating station.

A landfill that was under construction at the site, which was meant to hold coal ash lined terraces, ruptured over the weekend, spilling enough material to fill 180 dump trucks, according to the Associated Press.

The site received more than 30 inches of rain from Hurricane Florence, with the Cape Fear River expected to crest Saturday.

Duke Energy said Wednesday that water samples collected by its employees and tested at their own lab showed “no evidence of a coal ash impact” to the reservoir or the river. However, The Associated Press reported the samples did detect coal ash in wetlands adjacent to the shoreline.

North Carolina officials also received reports of earthen dam breaches at hog lagoons, spilling out feces and urine. Officials warned of possible contamination ahead of Florence.

Millions of chickens and turkeys and 5,500 hogs have been killed due to floodwaters.

The Associated Press contributed to this report.