Three coal-fired power plants in South Carolina have polluted rivers and endangered the health of people living nearby because the state’s environmental protection agency hasn’t done its job, according to a lawsuit filed Thursday.

The Sierra Club suit says the S.C. Department of Health and Environmental Control let water discharge permits expire for the power plants without taking steps to issue new — and tighter — limits on pollution released to rivers southeast of Columbia, north of Charleston and south of Georgetown.

The permits have been expired for 8 to 10 years, depending on the plant, the suit says.

Many of the people potentially impacted by DHEC’s failure to process the water permits are low-income and minority residents who live near the plants, the environmental group said in a news release Thursday.

DHEC’s failure to act has allowed “the plants to continue to discharge unacceptable amounts of toxic pollution into the waters of the United States,’’ the lawsuit said.

The power plants are operated by Dominion Energy of Virginia and Santee Cooper, a state owned utility with headquarters in Moncks Corner.

Dominion’s coal-fired power plant, for years a source of pollution complaints in southeast Richland County, discharges to the Wateree River near Eastover. The company said this week it has applied for a new discharge permit but DHEC has not acted.

Santee Cooper’s Cross generating station discharges to the diversion canal at Lake Moultrie north of Charleston, while its Winyah station discharges to a creek that flows to the North Santee and Sampit rivers below Georgetown. Santee Cooper has applied for a new permit and is following requirements to protect the environment as it awaits action by DHEC, power company spokeswoman Mollie Gore said.

DHEC had no comment Thursday, but Sierra Club officials said the suit was necessary because the state agency has failed to make decisions that could have protected the streams and people in the community. The Sierra Club wants DHEC to make a decision on the permits.

“The people responsible for making sure our communities are safe and our water is clean have failed us,” said the Sierra Club’s Xavier Boatright, who lives near the Cross plant.

“Black people, people of color and low-income South Carolinians shouldn’t have to beg for basic environmental and health protections that are rightfully ours.”

Coal-fired power plants have historically been among the biggest sources of pollution to air and water across the United States and in South Carolina, in many cases releasing toxic mercury and arsenic into the air, rivers or groundwater.

Mercury has a particularly toxic effect on fish, making some species too dangerous for people to eat in more than small amounts. Arsenic, a substance used historically as a poison, can sicken people whose drinking water is tainted by the material.

Many coal-fired power plants across the country were built decades ago in low-income and minority communities that had little voice in opposing construction or in later forcing power plants to clean up their acts, critics have said. Some people who live near coal plants fish for food in rivers near coal plants.

The suit said some Sierra Club members also are threatened by discharges from the expired permits.

“Members are deterred from recreating in these waters due to their knowledge the waters are contaminated and have observed posted signs relating to mercury contamination in the fish,’’ the suit said.

By federal law, industries that want to release pollution into the air or rivers need permits that limit how much can be discharged. But the permits must be renewed periodically, and in many cases, the pollution limits can be tightened by state agencies that administer the federal laws.

That didn’t happen with the three coal plants, the suit says.

Water discharge permits for Santee Cooper expired in 2010 at the Cross station and in 2011 at the Winyah station.The water discharge permit for Dominion’s Wateree plant expired in 2012, according to the suit.

The power companies applied for renewals but DHEC didn’t act, the Sierra Club says. Permits in this case are known as NPDES permits.

The suit comes after years of successful efforts by environmentalists to force the clean-out and closure of coal waste basins at all of the state’s power plants. The effort has been successful, with some — including Wateree’s basins — already cleaned out and others on schedule for it.

But while ash basins are closing, the coal plants still release other pollution to rivers and waterways nearby, experts say.

The issue of expired permits has surfaced at DHEC in the past.

In 2012, the agency revealed that some 500 environmental permits of all types had expired after then-director Catherine Templeton raised questions. The bulk of the expired permits were for water and air pollution discharges.

Frank Holleman, a lawyer with the Southern Environmental Law Center, said the Sierra Club’s actions to force DHEC to act on the coal plant permits appear warranted. He is not involved in the suit against the agency, but has had experience with DHEC’s handling of water discharge permits.

Holleman noted that a 2015 federal rule put stricter standards on water discharges. But if a permit isn’t renewed, a company continues to go by the old rules that are less stringent than they could be, he said.

“These permits are supposed to get tighter over time,’’ he said. “The goal of the Clean Water Act is not to permit pollution, but to eliminate pollution.’’

Contamination from the Wateree plant was the subject of court challenges in 2008 and 2012, the latter of which Holleman filed.

The plant’s coal-ash ponds have been cleaned out as a result of the suit, but Holleman said the facility still has other pollution discharges to the Wateree River. Holleman also used an overdue pollution discharge permit to force the cleanup of a coal ash pond on the Waccamaw River west of Myrtle Beach.

Dominion, which is not named as a defendant in the suit, said it applied for a new permit but it is up to DHEC to make a decision.

Dominion said it is following the rules at the Wateree coal plant.

“A complete and timely renewal application for Dominion Energy’s NPDES permit was submitted to DHEC,” Dominion spokesman Matt Long said in an email. “The NPDES permit continues in effect and Dominion Energy remains in complete compliance with the permit.”

Santee Cooper, which also is not named as a defendant, said it also is following the rules.

The company “did apply for permit renewals in a timely manner,’’ Gore said in an email. “Until new permits are issued, our existing permit remains in force and we are continuing to operate according to the terms of those existing permits. The requirements in those permits were established to protect human health and the environment at the time, and they continue to do so today.’’

The S.C. Environmental Law Project filed the suit on behalf of the Sierra Club.

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