BOULDER CITY, Nev. – Federal, state and tribal water managers are marking completion of a long-negotiated plan for 40 million people and vast irrigated farms to share crucial Colorado River water despite ongoing drought in the arid U.S. Southwest.

Interior Department official Tim Petty, Bureau of Reclamation chief Brenda Burman and representatives from seven states met Monday at Hoover Dam to commemorate an agreement spurred by nearly 20 years of drought and shrinking reservoirs.

President Donald Trump signed the so-called “drought contingency plan” last month.

Arizona, California, Colorado, Nevada, New Mexico, Utah, Wyoming and Mexico are affected.

The agreement aims to keep the key Lake Mead and Lake Powell reservoirs from getting so low they can’t produce hydropower or deliver water for cities including Los Angeles, San Diego, Denver, Phoenix and Las Vegas.