Coal ash from the dump of a power plant could be flowing into Cape Fear River in Wilmington in the US state of North Carolina.

Floodwaters from Hurricane Florence on Friday breached a dam holding back a large reservoir at the the LV Sutton Power Station and waste could be entering the river, which is nearby.

Gray material the company characterized as "coal combustion byproducts" could be seen floating in the lake and river.

Earthjustice, an environmental advocacy group with a boat in the river, provided The Associated Press with images Friday showing wide gray slicks in the water.

A team member plucked a turtle from the muck and rinsed it off.

Duke Energy spokeswoman Paige Sheehan said the utility doesn't believe the breach at the power plant poses a significant threat to nearby communities.

Floodwaters breached several points overnight in the earthen dam at Sutton Lake, the plant's 445-hectare reservoir.

Lake water then flooded one of three large coal ash dumps lining the lakeshore.