The U.S. Environmental Protection Agency (EPA) released a 338-page draft scientific study on the potential impacts of mining on the Bristol Bay watershed in southwestern Alaska that said large-scale salmon habitats may be harmed by mining near Bristol Bay.

Dennis McLerran, administrator of Seattle-based EPA region 10 told reporters that the chance of collapse from an earthen or rock-filled dam built to retain mine tailings is relatively small under standard engineering or state-of-the-art practices. However, if a collapse it did happen, it could degrade salmon-producing rivers and streams for decades The Anchorage Daily News reported.

The Kvichak River, part of the Bristol Bay watershed in southwest Alaska, produces more sockeye salmon than any other river in the world, according to the EPA. A subsidiary of London-based Anglo American and an affiliate of Vancouver-based Northern Dynasty Minerals Ltd. (NDM) formed a partnership in 2007 to work on the Pebble Mine project.

The Pebble Mine prospect area, in the watershed, has one of the world’s largest concentrations of three metals, with 80.6 billion lbs of copper, 5.6 billion lbs of molybdenum and 107.4 million oz of gold, according to the Pebble partnership’s web site.

The EPA said it studied the potential effect of mining in response to the companies’ announced plans and widespread interest among residents. The draft report will be circulated for comment.

Even if a large mine operated smoothly, with no engineering failures and no human-caused disasters, the EPA said in its analysis that miles of salmon rivers and streams could be lost or blocked, as could thousands of acres of wetlands that are vital to juvenile salmon.

The Pebble Partnership, the group behind the mine project, said the EPA’s review was rushed, speculative and “a federal intrusion.” It “could have a chilling effect on future resource development investments in Alaska,” Pebble said in a written response.