(CNN) In a surprise reversal, the Environmental Protection Agency announced it is withdrawing its plan to suspend environmental protections for an area of Alaska that is home to the world's most valuable wild salmon fishery.

The EPA proposed last year to "reverse clean water safeguards" for the Bristol Bay watershed, paving the way for a massive gold and copper mine to be built in the region.

The controversial proposal would have canceled an EPA protection put in place during the Obama administration. After years of study, the EPA found in 2014 that a mine "would result in complete loss of fish habitat" in some areas of the bay, and that "all of these losses would be irreversible."

The Bristol Bay watershed is one of the most pristine ecosystems in the world, supplying about half of the world's sockeye salmon.

CNN investigation last fall found that EPA Administrator Scott Pruitt ordered his staff to reverse the environmental protection within hours after meeting with the CEO of the mining company, Pebble Limited Partnership. Shortly after CNN's report, more than 40 congressional Democrats wrote a letter expressing "deep concern" about the EPA's reversal.

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