Unrelenting drought and years of rising temperatures due to climate change are pushing the long-overallocated Colorado River into new territory, setting the stage for the largest mandatory water cutbacks to date.

Lake Mead, the biggest reservoir on the river, has declined dramatically over the past two decades and now stands at just 40% of its full capacity. This summer, it’s projected to fall to the lowest levels since it was filled in the 1930s following the construction of Hoover Dam.