The Northwest Indian Fisheries Commission and the Nisqually Tribe near Olympia confirmed his death. The cause was not immediately known.
"He was a selfless leader who dedicated his life to the long fight for the rights of our state's native people," Gov. Jay Inslee said in a written statement. "Billy was a champion of tribal rights, of the salmon, and the environment. He did that even when it meant putting himself in physical danger or facing jail."
Frank was first arrested for salmon fishing as a boy in 1945 — an event that led him on a long campaign for tribal rights. He and others were repeatedly arrested as they staged "fish ins" demanding the right to fish in their historical waters, as they were guaranteed in treaties when they ceded land to white settlers in the 19th century. Frank was jailed more than 50 times.
The efforts were vindicated in 1974, when U.S. District Judge George Boldt affirmed the tribes' right to half of the fish harvest — and the nation's obligation to honour the old treaties.
Over the next 40 years, Frank continued to advocate for tribal fishing rights and protection of natural resources, including salmon.
Only weeks ago, he and other tribal members met with federal environmental regulators to push for more stringent water quality standards to reduce the amount of pollution that accumulates in fish. The standards would especially protect native people who eat large amounts of salmon and other fish from Washington state waters.
Merye Hayes, fisheries policy liaison with the Suquamish Tribe, knew Frank for 25 years.
"He's been so inspiring to all the tribes," Hayes said. "He believed in the work that he was doing. He will be missed by the tribal people and people who believe in the resources that he so wanted to protect."