Flooding caused by Hurricane Florence has breached a dam at a closed coal plant, raising the possibility that coal ash stored in an adjacent pit could leak into the Cape Fear River.

Duke said Friday that floodwaters were continuing to overflow an earthen dike at the north side of Sutton Lake, a man-made reservoir that supplies cooling water to the L.V. Sutton Plant in Wilmington, N.C.

That overflowing water, which began Thursday, has caused breaches in a dam on the south end of the lake that is flowing back into the Cape Fear River. The breach also forced Duke to shut down the 625-megawatt natural gas plant that now operates at Sutton after the coal plant retired in 2013.

The cooling lake does not store coal ash. But the reservoir is located next to two pits that do store coal ash.

[Also read: Hurricane Florence could flood many waste sites, creating toxic brew]

Coal ash might be escaping from one of the storage sites and polluting the river – Duke can’t say for sure.

“We can't say definitively what's in the water at this moment in time,” Shannon Brushe, a Duke spokeswoman told the W ashington Examiner on Friday. Brushe said the utility is in the process of collecting water samples from the river.

So far, Duke has found cenospheres – lightweight, hollow beads comprised of alumni and silica that are a byproduct of coal combustion – in the river, a sign that coal waste has entered the river.

Coal ash is the toxic waste left over from burning coal for electricity production.

Environmentalists have criticized the Trump administration for reconsidering an Obama-era rule that imposed new standards on coal ash disposal sites by increasing inspection and monitoring levels, and requiring power plants to install liners in new waste pits to prevent leaking that could threaten nearby drinking water supplies.