Josh Collins, an aquatic ecologist, uses a shocker unit to help find crawfish in the South River near Dooms, Va., on April 28, 2006. (Mike Tripp/Associated Press)

DuPont agreed Thursday to pay about $50 million to settle claims stemming from the release of mercury from a Shenandoah Valley plant in the 1930s and ’40s.

The heavy metal emitted from the Waynesboro, Va., facility persists in the environment, contaminating 100 miles of river and floodplain, state and federal officials said as they announced the proposed settlement. It still needs federal court approval.

If finalized, it would be the largest natural-resource damage settlement in state history and one of the largest of its kind nationwide.

Gov. Terry McAuliffe and Attorney General Mark R. Herring, both Democrats, joined officials with the U.S. departments of Justice and Interior to unveil the deal in Virginia’s Capitol.

They praised DuPont, which did not send a representative to the announcement, for its willingness to settle the case. Assistant U.S. Attorney General John C. Cruden called the company “extremely cooperative.”

Mike Liberati, South River project director for the DuPont Corporate Remediation Group, said the company has worked for years with state and federal authorities to determine if the plant harmed the environment.

“In keeping with its long history of cooperation with, and participation in, government initiatives, and its ongoing support of the local community, DuPont is committed to a long-term presence in the Waynesboro area and to maintaining transparency with its citizens,” he said in an email.

While producing rayon decades ago, the E.I. du Pont de Nemours and Company plant released mercury into the South River and South Fork Shenandoah River. Monitoring conducted over the past 20 years shows that mercury levels have not decreased.

DuPont has been working with officials since 2005 to assess the damage and identify potential restoration projects, state and federal officials said.

Under the proposed settlement, DuPont would provide $42 million for projects intended to make the environment and public whole. The company also would bankroll renovations to the Front Royal Fish Hatchery, a project expected to cost up to $10 million.

“Today’s settlement, the largest of its kind in Virginia history, is the culmination of a coordinated effort by countless partners at both the state and federal level,” McAuliffe said. “Thanks to their hard work, Virginians and the environment will benefit from unprecedented investments in land conservation and habitat restoration.”

Herring said the settlement will help the state protect the environment for future generations. “This settlement will allow us to protect and enhance lands throughout the Shenandoah Valley and improve the quality of water for wildlife, anglers, paddlers and others who use these waterways for recreation,” he said.