(Photo via usbr.gov)

Arizona's portion of the Colorado River depends on the level in Lake Mead.

Arizona's largest cities have reached a new water-sharing agreement. It’s an effort to support declining levels at Lake Mead and reduce water shortages.

The arrangement means that part of Phoenix's Colorado River water supply will be stored in the Tucson area next year, while Tucson will leave a portion of its supply in Lake Mead.

Phoenix will also store more of its Central Arizona Project supply than originally planned in an underground aquifer in the Tucson area, allowing Tucson to put more water into recharge basins.

Phoenix will still have access to the same share from the Central Arizona Project in the event of a Colorado River shortage.