BETHEL, Alaska (AP) — A feasibility study is being finalized for a multimillion-dollar clean up at the Red Devil mercury mine in the middle Kuskokwim River area.

Mercury, arsenic and antimony have been leaking into the Kuskokwim River for years from 250,000 cubic yards of tailings, waste produced by removing valuable substances from ore. The state has warned subsistence fishermen not to pull fish from the area.

The Bureau of Land Management may fence off the tailings. Red Devil project manager Mike McCrum said other options include excavating the Red Devil Creek valley and removing the tailings and effected soil.

“In the end the most important thing is to address the tailings,” McCrum said. “They’re still piled up next to Red Devil creek, and that’s not a good place for them to be. The issues we’re working on now are not whether we’re going to do anything. The issues are more: what are we going to do, what’s the most efficient and optimal thing to do.”

A $285 million plan to haul out the tailings on barges is about six times more expensive than keeping the tailings on-site.

“It’s common to simply remove them from the location where they’re creating an environmental issue,” McCrum said. “In this case it’s being near the water, it’s the aquatic ecosystem that’s the most sensitive to the metals being released by the tailings. So, getting those tailings up and away from the water is probably the single most important thing you can do.”

Officials are planning to ask residents to provide input early next year.