Floodwaters from Hurricane Florence caused a dam to breach in North Carolina, potentially allowing coal ash to flow into a major river.

The earthen dam separating Sutton Lake from the Cape Fear River breached near Wilmington, N.C., the Associated Press reported, citing Duke Energy Corp., the owner of the adjacent power plant and coal ash pond.

Water had previously overtopped the dam separating the lake from the coal ash ponds for the L.V. Sutton Power Station, so the ash might now get into the river, AP said.

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Duke spokeswoman Paige Sheehan said because of the levels of water due to the flooding, she did not expect the water level in the lake to drop, which would mean a large outflow of potentially contaminated water.

Coal ash is a waste product from burning coal. It is not considered toxic by the Environmental Protection Agency, but it contains heavy metals like arsenic and cadmium, and its disposal is federally regulated.

The breach came days after Duke reported that floodwaters had displaced about 180 truckloads of coal ash from a nearby pond.

Another North Carolina Duke plant was the site of a major 2014 coal ash spill caused by a rupture in a drainage pipe. The company ended up admitting fault and paying more than $100 million in fines and restitution for that incident.