SAN FRANCISCO — A U.S. federal appeals court said that national wildlife rules bar the stocking of salmon in a protected Alaskan lake, even if little harm comes from multiplying the fish.

For nearly 20 years, the Alaska Department of Fish and Game has incubated salmon eggs and released millions of young fish into the Tustumena Lake in the Kenai Refuge, a protected wildlife area.

The Wilderness Society and the Alaska Center for the Environment sued over the stocking, saying it violated the U.S. Wilderness Act which bars commercial activity in wildlife areas. The 9th Circuit Court of Appeals based in San Francisco agreed and on Tuesday reversed a lower court ruling.

"The Wilderness Act requires that the lands and waters designated as wilderness must be left untouched, untrammeled, and unaltered by commerce," Judge Ronald Gould wrote.

"By contrast, the Enhancement Project is a commercial enterprise within the boundaries of a designated wilderness and violates the Wilderness Act."

The en banc panel of 11 judges found that there could be worse things than stocking fish in a lake, but still held it was not permissible under the Wilderness Act.

"We deal the activity with a benign aim to enhance the catch of fishermen, with little visible detriment to wilderness, under the cooperative banner of a non-profit trade association and state regulators," the decision read.

"Surely this fish-stocking program, whose antecedents were a state-run research project, is nothing like the building of a McDonald's restaurant or a Wal-Mart store on the shores of Tustumena Lake."

"Nor is the project like cutting timber, extracting minerals, or otherwise exploiting wilderness resources in a way that is plainly destructive of their preservation."

The court noted that the program raised money by selling off surplus young fish and by imposing a voluntary tax.

"The primary purpose of the Enhancement Project is to advance commercial interests of Cook Inlet fishermen by swelling the salmon runs from which they will eventually make their catch," the judges found.

A few hours' drive south of Anchorage, the Kenai refuge counts more than half a million visitors each year, attracting about three-quarters of all the people who travel to Alaska's 16 national wildlife refuges.