Top federal water managers plan to meet with officials from Indian tribes, conservationists and seven Western states to begin shaping rules for squeezing every useable drop from the overtaxed Colorado River.

The meeting Tuesday in San Diego comes amid dire predictions of looming shortages.

Just five months ago, the secretary of the interior declared the Colorado River might not be able to meet demands of a growing regional population over the next 50 years.

Federal Bureau of Reclamation Commissioner Michael Connor now says 2013 could be the fourth-driest year in the basin in the past 100 years. Last year was the fifth-driest.

The river is crucial to 40 million people in California, Arizona, Colorado, Nevada, Utah, New Mexico and Wyoming. Mexico also has a stake, and by treaty must get a set amount of water from the Colorado.