Arizona was the only state that required legislation to join the agreement to protect the water that serves 40 million people in Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada and California.
The drought plan requires Arizona to find a way to reduce its use of Colorado River water by up to 700,000 acre-feet — more than twice Nevada's yearly allocation under the drought plan.
The other six states in the Colorado River basin have agreed to plans that recognize a long-running drought, the dwindling supply of water and how they intend to cope with it.
Since the first locomotive steamed through the canyon, the train has been the best way to see the vistas — mostly because someone else is driving.
Cloud seeding technology remains tricky and expensive, but has become more vital as the effects of climate change ramp up.
Revving up the legal gears could pose a setback for Denver Water, which has spent years securing the necessary permits.
A deal was supposed to be signed by the end of 2018, under threat that the water levels on the river would push the federal government to impose its own restrictions.
Colorado River water supports about 40 million people and millions of acres of farmland in the U.S. and Mexico.
In 1991, federal officials classified the razorback sucker as an endangered species.
The long-waited announcement comes as the river's two largest reservoirs, Lake Mead and Lake Powell, have been drained to alarmingly low levels.