CHARLESTON — Conservation groups in two states say a federal judge needs to decide now, not later, whether the U.S. Army Corps of Engineers needs a South Carolina pollution permit for the $650 million deepening of the Savannah River shipping channel.

The groups earlier sued saying the long-awaited deepening of the 38-mile channel will dredge up toxic cadmium in river silt that will be dumped on the South Carolina side of the river dividing the state from Georgia.

The corps earlier asked U.S. District Judge Richard Gergel to dismiss the suit, saying the plaintiffs have not been harmed and the case is premature.

“Plaintiffs need not wait for environmental injury to be consummated before exercising their rights to prevent it,” attorney Blan Holman representing the Southern Environmental Law Center wrote in a response filed late Tuesday.

The lawsuit was filed by the center on behalf of the Savannah Riverkeeper based in Augusta, Ga., the South Carolina Coastal Conservation League and the South Carolina Wildlife Federation. The deepening is being sought so the Georgia ports can larger container ships that will routinely be calling when the Panama Canal is deepened in 2014.

Holman noted the corps applied for other South Carolina approvals two years ago and waiting until work begins before deciding on whether a pollution permit is needed is too late.

“Indeed, the corps would require the Savanna River to be dredged to an irreversibly damaging depth before any court could intervene,” he added, saying the plaintiffs have standing to sue because the corps is nearing the end of a decade long study process. He added that issuing a pollution permit involves public notice and participation and abridging those rights constitutes an injury to the plaintiffs.

A spokesman for the corps’ Savannah District said the agency does not comment on pending lawsuits.

A state lawsuit brought by the same plaintiffs as well as the Conservation Voters of South Carolina was heard earlier this month by the South Carolina Supreme Court.

That suit alleges a permit approved by the Department of Health and Environmental Control last year is illegal authority over river dredging decisions rests with the state Savannah River Maritime Commission.

Chief Justice Jean Toal said during a hearing that DHEC broke state law when it shut out the river commission dredging negotiations and the agency “rubber stamped” an agreement with Georgia officials.

DHEC staff had initially turned down the permit, but the agency reversed itself after Georgia Gov. Nathan Deal flew to Columbia to meet with Gov. Nikki Haley, who appoints members of the DHEC board.