The runoff will put so much water into the Colorado River that Lake Powell is expected to rise 50 feet this year.
Snowpack and a slow melt could combine for good water recreation in all parts of the state.
Representatives from the seven states that rely on Colorado River water met at the Hoover Dam to mark a long-negotiated agreement aimed at keeping reservoirs from drying up.
In early February, southwestern McPhee Reservoir was 7 percent full. Now it’s a quarter full and expected to fill up all the way.
A snowy winter and wet spring mean more of Colorado’s snowpack will make it into reservoirs across the Colorado River System.
The seven-state drought contingency plan seeks to keep two Colorado River reservoirs from dropping so low they cannot deliver water or produce hydropower.
The legislation had the support of all 14 senators representing the Colorado River basin states.
The U.S. House and Senate approved the Colorado River drought contingency plan on Monday.
Scientists are studying how much water is lost to evaporation at the nation's two largest reservoirs. There's no stopping it, but more accurate measurements could lead to better water budgeting on the Colorado River.
Colorado River basin states want congressional approval by April 22 so that Mexico also will contribute water starting in 2020.