http://www.sciencemag.org/news/2020/08/reversal-trump-kills-huge-alaskan-gold-mine-here-s-why

The U.S. Army Corps of Engineers today asked the Pebble Partnership to submit plans for offsetting the damage its giant proposed copper and gold mine would cause to thousands of acres of wetlands and streams in southwest Alaska's Bristol Bay region—a hurdle that could delay and ultimately thwart federal permitting.

The Army Corps' Alaska District found that "discharges at the mine site would cause unavoidable adverse impacts to aquatic resources and, preliminarily, that those adverse impacts would result in significant degradation to those aquatic resources."