Gray wolves are being fatally poisoned in the remote northeast corner of Washington state, according to state wildlife officials, who said Monday that six have been found dead.
Two carcasses were discovered recently and four were found in February, the state Fish and Wildlife Department reported.
"Toxicology results revealed all six wolves died from ingesting poison," the department said.
Fish and Wildlife police have been investigating since last year.
Gray wolves are listed by the state as endangered, and they're federally endangered in the western two-thirds of the state.
Killing animals that belong to an endangered species in the state is a misdemeanor, and defendants face the possibility of a year in jail and a fine of up to $5,000.
Nonprofit groups have contributed to a reward for information leading to the arrest and conviction of anyone responsible in the wolves' deaths. It was at $51,400 Monday.
Defenders of Wildlife said it contributed $2,500 to the collection. Zoë Hanley, the group's wolf biologist, said the deaths were "a tragic, unnecessary loss."
"This cowardly act flies in the face of committed efforts from biologists, policymakers and ranchers working to recover and coexist with wolves in Washington," she said in a statement.
The wolves, part of the Wedge pack, roam the northeast part of the state in Stevens County.
Fish and Wildlife officials said there were 206 known wolves in 33 packs in Washington at the end of 2021.