Despite strong support from community groups and local businesses, U.S. Environmental Protection Agency (EPA) officials have ruled against large-scale mining in Alaska’s Bristol Bay, saying it could spoil wetlands and streams, local fishing habitats and subsistence-based populations.

The decision was controversial for favoring a hypothetical study over a future permit plan submitted by the Pebble Mine Partnership. The alliance, along with industry and community groups, and backed by the National Mining Association (NMA), said EPA officials, effectively pre-empted mining opportunities in the area’s prolific copper and gold reserves.

Pebble Partnership CEO John Shively said the ruling was based on a “poorly conceived and poorly executed study;” partnership representatives have reported spending more than $600 million in engineering and environmental studies.

The EPA following drafts in 2012 and 2013, moreover, ignored “critical” environmental safeguards and “mitigation measures state and federal permits will require,” the partnership added in a statement, “nor has it examined the most advanced engineering and mining practices that would be used.”

Sen. Mark Begich (D-Alaska), meanwhile, broke with the state’s congressional delegation by announcing his opposition to large-scale mining ahead of fall’s elections. The partnership, accordingly, responded “we are stunned an Alaskan senator supports the EPA … to make decisions about future development on state land in Alaska.”