Why Arizona is suing

Arizona has joined Nevada in its legal battle against the Trump administration's proposed cuts to the states' shares of the shrinking Colorado River, Governor Katie Hobbs said in a Friday statement.

Hobbs said she acted because the federal government refuses to hold the Upper Basin accountable for the water deliveries it owes Arizona and threatens cuts beyond the Lower Basin Agreement, a two-year voluntary water conservation pact among her state, California and Nevada. In her words, the state is drawing a line in the sand.

The proposed cuts

This summer the interior department announced restrictions that could slash the water supplied to the lower basin states - Arizona, California and Nevada - over the next two years, depending on the river's condition. The upper basin states were spared:

• Wyoming
• Colorado
• Utah
• New Mexico

Crisis behind the dispute

Lake Mead and Lake Powell have plummeted to historically low levels because of overuse and a changing climate. The states reached an impasse, with upper basin states arguing their downstream counterparts were responsible for the reservoir's water shortages and should face the largest cuts. Washington stepped in after the states missed several deadlines for a consensus. Officials fear that if levels fell far enough the waterway would effectively stop flowing downstream, a condition known as deadpool.

Protecting legal rights

Tom Buschatzke, director of Arizona's water department, said the move preserves cooperation with California and Nevada while defending the state's share. "intervention in the Nevada lawsuit is necessary at this time for Arizona to protect its legal rights to Colorado River water," he said.

An interior department spokesperson did not immediately respond to a request for comment on the joint litigation.