The U.S. and Mexico may have a deal for future scarcity of Colorado River water, but several U.S. states still have to work out agreements with each other.  

The binational treaty extension lets the two countries adjust where Colorado River water goes when Lake Mead runs low. Lake Mead is one of the main reservoirs for the Colorado. This flexibility is meant to keep Lake Mead above a certain threshold and avoid mandatory water cutbacks.

Arizona State University law professor Rhett Larson is a fan of the deal, but pointed out there are other Colorado River negotiations.

“While it’s great news for relationships between the United States and Mexico, it places a lot of pressure on the lower basin states Arizona, California, and Nevada to come to an agreement between themselves,” he said.

Larson added that water laws governing the lower basin states are more rigid than U.S. and Mexico treaties. Because of that, interstate water negotiations are harder than the just-finished binational talks.

Tom Buschatzke, Arizona’s director of Water Resources, said the so-called “Drought Contingency Plan” for the lower-basin states is more or less done. But Arizona and California have some internal work to do.

“Within Arizona, it’s issues regarding the impacts to various water user groups — homebuilders and developers, agricultural tribes and cities — who are all disproportionately impacted by the additional reductions that will occur in Arizona,” he told reporters after the Minute 323 announcement on Wednesday.

Buschatske said these details need to be settled before Arizona can ink its deal with California and Nevada.