RALEIGH, N.C. — Federal authorities have launched a criminal investigation into a massive coal ash spill into a North Carolina river, demanding that Duke Energy and state regulators hand over reams of documents related to the accident that left a waterway polluted with tons of toxic sludge.

The U.S. Attorney’s Office in Raleigh issued grand jury subpoenas seeking records from Duke and the North Carolina Department of Environment and Natural Resources. The subpoenas seek emails, memos and reports related to the Feb. 2 spill into the Dan River and the state’s oversight of the company’s 30 other coal ash dumps in North Carolina.

The Associated Press obtained a copy on Thursday of the subpoena issued to the state through a public records request.

“An official criminal investigation of a suspected felony is being conducted by an agency of the United States and a federal grand jury,” said a cover letter accompanying the subpoena, which was dated Monday and signed by a criminal prosecutor.

The exact crime and precisely who is being targeted for potential prosecution is not spelled out in the document.

A Duke spokesman confirmed the nation’s largest electricity provider had also received a subpoena.

Thomas Walker, the U.S. Attorney for the Eastern District of North Carolina, said he could not comment on the subpoenas.

The spill at a Duke Energy plant in Eden spewed enough toxic sludge to fill 73 Olympic-sized pools, turning the river water a milky gray for miles. It was the third-largest coal ash spill in U.S. history.

State health officials have advised that people not eat fish from the river and avoid contact with the water. Coal ash contains arsenic, lead, mercury and a host of other chemicals that are highly toxic to humans and aquatic life.

In addition to the demand for records, prosecutors also ordered the state environmental agency’s chief lawyer to testify next month before a grand jury. Agency spokesman Drew Elliot said the state will fully cooperate with the federal investigation.

Duke Energy spokesman Thomas Williams said the company doesn’t comment on pending litigation but said officials would cooperate with any investigation.

The subpoenas were issued the day after the AP reported that environmental groups have tried three times in the past year to sue under the Clean Water Act to force Duke to clear out leaky coal ash dumps.

Each time, the state agency blocked the citizen lawsuits by intervening at the last minute to assert its own authority under the act to take enforcement action in state court.