BILLINGS, Mont. — State officials have issued a draft operating permit for an underground copper mine in central Montana that opponents worry could harm one of the state’s most popular fly-fishing destinations.

Tintina Resources said Tuesday that a third-party contractor will be hired to study environmental impacts of the Black Butte mine near White Sulphur. Under state law the review of the project must be done within one year.

The company says the mine would employ about 240 people and remove 1.3 million tons of rock annually.

The Montana Department of Environmental Quality says the project needs additional air and water quality permits.

Conservation groups are concerned about potential pollution into a tributary of the Smith River, which is so popular among boaters that the state conducts an annual lottery to regulate access.