(CNN) Coal ash is likely entering the Cape Fear River in Wilmington, North Carolina, environmentalists said Friday. Rising water in the area, due to heavy rain and storm surge from Hurricane Florence, is still a problem.

Duke Energy confirmed breaches to a cooling lake dam at its L.V. Sutton plant in Wilmington, although it said coal ash -- industrial waste created by coal-burning power plants -- is probably not moving into the river.

The state has been closely monitoring conditions at the facility. Since Thursday night, high water from the Cape Fear River has flowed into Sutton Lake on the north side and into the river on the south side. On Friday morning, state dam safety officials were notified of a dam breach of between 100 and 200 feet at the south end of Sutton Lake. There may also be smaller breaches in the dam, according to the state.

"The Cape Fear River has spilled into the Sutton Lake. It has spilled over into their transmission yard. Duke has evacuated their employees," Michael Regan , secretary of the North Carolina Department of Environmental Quality, said Friday. "What we don't know at this point is if any coal ash has filtered into the Cape Fear River."

The department said it is working with other agencies to monitor the situation. It plans to conduct flyovers as well as on-the-ground testing and drone inspections of the dam.

Duke Energy spokeswoman Paige Sheehan confirmed that nine employees were at the plant overnight, although "they safely left as the flooding began to occur." The team included regular plant operators and some employees sent to monitor the situation after the hurricane, she said.

"They left the plant itself but stayed nearby the property on higher ground," she added. Additional engineering experts are being brought in to assist with the situation, and large stones are being added to stop the breach.

"Although river flooding has approached the two inactive coal basins at the facility, it appears there are currently no structural issues with those impoundments," said Bridget Munger, deputy communications director for the North Carolina Department of Environmental Quality, on Friday, noting that state teams from three regulatory divisions are on site.

Coal ash is one of the largest forms of industrial waste, according to the US Environmental Protection Agency . It contains heavy metals including arsenic, lead and mercury, which can pose serious health risks.

According to the EPA, exposure to coal ash waste "can cause severe health and environmental problems in the form of cancer and non-cancer risks in humans, lowered IQ among children, and deformities and reproductive harm in fish and wildlife. Many of these pollutants, once in the environment, remain there for years."

More immediate health risks could be respiratory, such as asthma.

Duke Energy said after the initial breach earlier in the week, "Coal ash is non-hazardous, and the company does not believe this incident poses a risk to public health or the environment."

In a news release, Duke said , "Cenospheres are moving from the 1971 ash basin to the cooling lake and into the Cape Fear River. Cenospheres are lightweight, hollow beads comprised of aluminum and silica that are a byproduct of coal combustion."

Lisa Evans, an attorney with the environmental group EarthJustice, said, "If these [cenospheres] have been released, it is likely that [coal] ash has also been released. We are still awaiting additional information, but in the 2016 hurricane [Matthew], Duke also referred only to cenospheres when ash was also present."

The group and other environmentalists are collecting samples to confirm the presence of coal ash in the water flowing from the cooling plant into the river. Those tests take 72 hours, and with the weekend, results are not expected until Wednesday.

It is not known what amounts of cenospheres or coal ash have entered the river, and therefore it is difficult to determine the potential health risks.

"Specific health concerns depend on the components of cenospheres: for example, whether there are arsenic or other heavy metals in cenospheres, and what are their concentrations," Dr. Julia Krauchanka wrote in an email. She studies the impact of coal ash on human health and is an assistant professor in the Department of Surgery, Division of Surgical Sciences at the Duke University School of Medicine.

The health effects of cenospheres from coal ash on human health "remain unclear."

"We can suppose that potential health impacts will depend on composition of cenospheres (type and concentration of heavy metals) and the way they can enter human organism (e.g., when consuming contaminated water)," Krauchanka wrote.

She added it's important to keep in mind that most coal ash sites in North Carolina are rated by the EPA as highly hazardous -- such as when a dam failure is likely to cause loss of human lives -- or as significantly hazardous -- as when a dam failure is likely to cause significant economic loss, environment damage or damages to infrastructure.

In North Carolina, there are additional concerns with these coal ash sites, Krauchanka said. Unlined impoundments in coal ash sites may not restrict toxic pollutants from seeping into surrounding groundwater, rivers and lakes, and impoundments that are in poor condition are more likely to leak and contaminate groundwater, surface water or surrounding property.

Extreme weather, as with Florence, "substantially increase(s) the risk of exposure in residential communities, including those located downstream the river," Krauchanka said. "While information about the health impact of coal-fired plants on human health remains sparse, health risks that have been reported include, but are not limited to, a spectrum of diseases such as increased risk of respiratory and cardiovascular diseases, respiratory cancer, low birth weight, higher risk of developmental and behavioral disorders in infants and children, and increased infant mortality."

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The state said that while it is still in emergency response mode, it will keep a careful eye on the impacts of the breach.

"A thorough investigation of events will soon follow to ensure that Duke Energy is held responsible for any environmental impacts caused at their coal ash facilities," Munger said.