(Bloomberg) -- Floodwaters have overwhelmed an ash basin at a Duke Energy Corp. power plant in North Carolina, spilling a byproduct of burning coal into the Cape Fear River.

The company said coal ash at the site “remains in place” but that tiny beads called cenospheres are flowing into the river. The hollow beads, left over from burning coal, are comprised of alumina and silica, Duke said in a statement Friday.

“Cenospheres are moving from the 1971 ash basin to the cooling lake and into the Cape Fear River,” the company said.

Peter Harrison, a staff attorney for the environmental group Earthjustice, said it’s misleading for Duke to draw distinctions between cenospheres and toxic coal ash. The spill, he said, could have serious consequences.

“It’s a major escalation,” Harrison said in an interview Friday. “Cenospheres are coal ash. To say that cenospheres are not coal ash is like saying a poodle is not a dog.”

Duke shares fell as much as 2.6 percent Friday.

If coal ash did flow into the Cape Fear river it “would be hardly measurable” because of all the rainfall, said Avner Vengosh, a Duke University professor who specializes in geochemistry and water quality. But even small quantities can harm fish and aquatic life, he said.

Coal ash, a byproduct from burning the fuel in power plants, can carry arsenic, mercury, lead and selenium, though its overall toxicity has long been debated.

Record floods cover much of eastern North Carolina in the wake of Hurricane Florence, and the waters are still rising. Emergency responders and companies like Duke will be dealing with the deluge for weeks after the storm made landfall in the state Sept. 14, according to the National Weather Service.

Duke activated a high-level emergency alert Thursday at the site in Wilmington, North Carolina, where the Cape Fear River overtopped the facility’s cooling pond, also know as Lake Sutton. The facility also includes a coal-ash landfill, and Duke told state officials earlier this week that some material has spilled into the cooling pond, according to Duke spokesman Bill Norton.

The company said Wednesday that initial tests show the coal ash spill “has not impacted water quality” in Sutton Lake.

Flooding also reached the footprint of Duke’s 626-megawatt natural gas plant at the site, prompting the utility to shut down the generator.

--With assistance from Rachel Adams-Heard.

To contact the reporter on this story: Jim Efstathiou Jr. in New York at jefstathiou@bloomberg.net

To contact the editors responsible for this story: Joe Ryan at jryan173@bloomberg.net, Will Wade

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