Arizona water officials tout their Colorado River drought plan as a historic step forward. Critics see drawbacks and missed opportunities. Diana Payan, The Republic | azcentral.com

The federal Bureau of Reclamation activated the mandatory reductions in water deliveries on Thursday when it released projections showing that as of Jan. 1, the level of Lake Mead will sit just below a threshold that triggers the cuts. 

Arizona and Nevada agreed to leave a portion of their water allotments in the reservoir under a landmark deal with California called the Lower Basin Drought Contingency Plan, which the states' representatives signed at Hoover Dam in May. 

California agreed to contribute water at a lower trigger point if the reservoir continues to fall. And Mexico agreed under a separate accord to start contributing to help prop up Lake Mead, which is now 39 percent full.

The Colorado River's reservoirs have dropped dramatically since 2000 during one of the most extreme droughts in centuries. Farms and cities across the Southwest have long been taking more from the river than what flows into it, and climate change is adding to the strains by pushing up temperatures. 

Reservoirs were approaching levels last year that would have triggered a shortage and required deeper cuts, but heavy snow across much of the Rocky Mountains this winter boosted runoff and raised reservoir levels. The river's reservoirs are now at 55% of total capacity, up from 49% at the same time last year. 

But Lake Mead is still projected to be just below the threshold of 1,090 feet above sea level at the beginning of next year. That will put the reservoir in a zone called "Tier Zero," at which the first cuts take effect.