Three Western states would face significant reductions in their use of Colorado River water under a new federal proposal intended to protect a critical water supply strained by decades of drought and overuse.

The federal government unveiled the 10-year proposal Friday following years of disagreements among the seven states that rely on the river. The plan would replace expiring operating guidelines.

Under the proposal, California would reduce its Colorado River water use by about 10%, Nevada by 16% and Arizona by 27%, according to Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University.

The limits would be reviewed every two years, allowing federal officials to respond to changing water levels and other conditions.

The Colorado River supplies water to about 40 million people and irrigates millions of acres of farmland. Years of drought, rising temperatures and demand exceeding the river’s supply have contributed to historically low levels at Lake Mead and Lake Powell, the country’s two largest reservoirs. Both also generate hydroelectric power.

For now, the four Upper Basin states — Colorado, Utah, New Mexico and Wyoming — would not be required to make reductions under the proposal. That distinction could prolong disagreements among the states over how to divide conservation responsibilities.

Officials from the Lower Basin states have indicated they hope negotiations will eventually produce a longer-term agreement involving all seven states. Legal challenges between states or against the federal government also remain possible.

Agriculture is likely to be particularly affected by reduced supplies. Farming uses most Colorado River water, with a substantial share used to grow crops such as alfalfa and other feed for livestock.

Water restrictions could also affect more than agriculture. Continued uncertainty about future supplies could complicate housing and commercial development in rapidly growing parts of Arizona and other Southwestern states.

Source: NYT