The US Environmental Protection Agency (EPA) is citing the Clean Water Act to safeguard the world's largest sockeye salmon fishery in Bristol Bay, Alaska, from the proposed Pebble Mine.
The Pebble project is situated in the Bristol Bay region in south-west Alaska, about 200 miles from Anchorage.
Pebble Mine, which would be North America's largest open pit copper mine, is said to present devastating environmental consequences to salmon and the tribal communities that have been dependent on them for thousands of years.
Although the EPA's action is not final and cannot block the project, the US Army Corps cannot take any steps to grant permits while section 404c of the Clean Water Act is under review.
EPA regional administrator Dennis McLerran said: "Bristol Bay is an extraordinary natural resource, home to some of the most abundant salmon-producing rivers in the world."
According to the EPA study in January, the proposed mine site would destroy up to 94 miles of streams and 5,350 acres of wetlands, lakes and ponds.
The EPA estimates that mining activity in the region would reduce the flow of 33 miles of salmon-supporting streams, which could affect the ecosystem's structure and function.
The project is being developed by the Pebble Limited Partnership, a 50-50 partnership between Anglo American and an affiliate of Northern Dynasty Minerals.
Anglo American Pebble chose to withdraw from the Pebble copper project in Alaska, US, in September.
Bristol Bay produces nearly 50% of the world's wild sockeye salmon, with runs averaging 37.5 million fish, annually.
Image: Map of Bristol Bay, Alaska. Photo: courtesy of Aconcagua.