Negotiations between the U.S. and Mexico to seal a water-sharing deal over the dwindling supplies on the Colorado River are confronting a new deadline: the inauguration of Donald Trump.

A 16-year drought has sent water levels at the river’s most important reservoir, Lake Mead, to their lowest point since it was first filled in the 1930s, threatening supply cuts for 40 million people across seven U.S. states and two Mexican states. It’s also raising the stakes for the two countries as they try to hammer out an extension of a four-year-old agreement on how to share the water.