A nonprofit environmental group is petitioning the U.S. Fish and Wildlife Service to list Utah's state fish, the Bonneville cutthroat, as a threatened species.

Rainbows and other nonnative fish are a major threat to the cutthroat and it deserves protection under the Endangered Species Act, says the Biodiversity Legal Foundation, based in Boulder, Colo.The foundation recently filed a 150-page petition with the federal agency's Salt Lake office.

The petition is part of a multistate effort by environmental groups to address dwindling numbers of cutthroat trout species in the Rocky Mountains, from Mexico to Canada.

Last year, the Legislature named the Bonneville cutthroat as the official state fish, replacing the nonnative rainbow trout.

The Bonneville cutthroat, which evolved in Lake Bonneville 20,000 years ago, exists in 147 miles of streams in Utah, Nevada, Idaho and Wyoming. It also can be found in Bear Lake.

The Bonneville cutthroat is threatened by hybridization and depredation from nonnative fish species, habitat destruction, water projects and degradation of water quality from mining, road-building, grazing and logging.

The FWS has resisted previous efforts to list the fish as endangered, preferring instead to work with state and private interests to protect the fish with a "conservation agreement" adopted in 1995.

Conservation agreements avoid an official listing, which can result in federal restrictions on land use.

The Bonneville cutthroat agreement has centered on locating stream segments containing pure strains of the fish. It also calls for eradicating nonnative species from some streams.

But Jasper Carlton, director of the Biodiversity Legal Foundation, is dubious. He says he has never seen an adequate conservation agreement.

"They are political statements of nice intent. They are voluntary, unenforceable and unaccountable," Carlton said.

Reed Harris, field supervisor for the FWS in Utah, said he believes the conservation agreement for the Bonneville cutthroat is sound. But he acknowledged it lacks funding. Harris said an endangered species mitigation fund created by the Legislature last year may help.

The Biodiversity Legal Foundation's petition likely will trigger a one-year "status review" of the Bonneville cutthroat. That review then will determine whether to add the Bonneville cutthroat to the endangered species list.

State and federal wildlife officials from Utah, Nevada, Idaho and Wyoming plan to meet in Salt Lake City on April 7 to discuss the petition.

Environmental and sport-fishing groups first sought the listing in 1979.