Upper Columbia River water rights will be “profoundly uncertain” until tribal rights to Lake Roosevelt, the state’s largest reservoir, are resolved, according to the Washington Department of Ecology.

At the formal request of one tribe and consent of another, Ecology plans to adjudicate rights to the reservoir. The reservoir backs up behind Grand Coulee Dam and supplies water to irrigate 671,000 acres of farmland.

The state’s three largest irrigation districts contract with the Bureau of Reclamation to receive water. The bureau’s rights date back to 1938, but are “potentially vulnerable to even older tribal claims,” Ecology stated in a report to the Legislature.

“The legal assessment of tribal water rights in the Upper Columbia River, particularly Lake Roosevelt itself, has been a missing piece of this entire management system,” according to Ecology.

A Reclamation spokeswoman on Oct. 29 said the federal agency was aware of the report, but was waiting for Ecology to act.

“Because there is currently no action for the Bureau of Reclamation to take, we are standing by until Ecology’s next steps are communicated,” she said in an email.

“At that time, we will begin working with the Department of the Interior and the federal government to develop our federal response.”

East Columbia Basin Irrigation District general manager Craig Simpson said he doesn’t anticipate the district will be directly involved in court proceedings, but will watch closely and support Reclamation.

“We are all wondering what this will do,” he said. “We don’t know what the implications will be.”

Lake Roosevelt borders the reservations of the Confederated Tribes of the Colville and the Spokane Tribe of Indians. The Colville tribe petitioned Ecology in 2019 to adjudicate Columbia River water rights.

Treaties promise tribes water for their reservations and to preserve off-reservation fishing and hunting, but the rights have not been quantified.

“An adjudication will serve the public interest by removing any uncertainties that result from the tribes’ outstanding claims to significant amounts of senior water rights,” according to the Colville petition.

Ecology calls adjudication a powerful tool to sort out water rights in a basin. The state’s only major adjudication case was filed in Yakima County Superior Court in 1977 and completely resolved in 2019.

Ecology has now turned its attention to Lake Roosevelt and the Nooksack River Basin in northwest Washington, anticipating the new adjudications would be done quicker, but still take more than 15 years.

The Nooksack adjudication will involve far more water-right holders. “However, due to the senior claims of the tribes to Columbia River Project water, this area is the most profoundly uncertain and vulnerable of any in the state,” according to Ecology.

The department has asked for $1 million to begin the adjudication cases. Even if lawmakers deny the funding request, Ecology will continue to prepare the cases, a department spokeswoman said. The Lake Roosevelt adjudication would most likely be filed in Spokane County Superior Court, she said.

Grand Coulee Dam controls the flow of the Columbia River, creating the 151-mile long Lake Roosevelt. Folk singer Woody Guthrie celebrated the dam: “I’ll settle this land, boys, and work like a man/I’ll water my crops from Grand Coulee Dam.”

Ecology’s report says that the agriculture, grazing, logging and development that followed the dam’s construction degraded habitat and caused an invasion of non-native species. Climate change models show conditions for habitat will worsen, according to Ecology.

The spokeswoman said climate change and declining habitat make adjudication urgent, but Ecology’s recommendations to the court will be based on a water right’s date, quantity, place and purpose.

“We do NOT balance between water users and fish,” the spokeswoman wrote in an email. “It is not a policy discussion.”