JUNEAU — The state of Alaska is fighting a U.S. Environmental Protection Agency study that looks at the potential impacts of mining on the world-class Bristol Bay salmon fishery.

The watershed assessment is a direct response to concerns that have been raised about the Pebble Mine project, a large copper-and-gold prospect near the headwaters of Bristol Bay. But Alaska’s attorney general, in letters to EPA regional administrator Dennis McLerran, has asked EPA to stop its work, claiming, among other things, that the agency’s actions are premature and an overreach.

Michael Geraghty, in a March 9 letter, said EPA has shared “little information about its purported legal authority” to conduct the study, and he raised concerns that it could lead to the agency vetoing mining activity. If EPA were to invoke a section of the Clean Water Act that allows it to restrict or bar use of certain waters for dredge or fill materials, that could have the potential to “extinguish” the state’s mineral rights and leases held by others, he said. Geraghty noted that the assessment encompasses about 15 million acres of largely state-owned land, an area that he says is comparable to the size of West Virginia.