Hamby said it is vital for states that use Colorado River water to reduce water use. Years of overuse combined with drought and rising temperatures have been depleting Lake Mead and Lake Powell, the country’s second-largest reservoir. Levels at Lake Powell have dropped so much that it has become difficult to descend far enough to reach the water. Lake Mead and Lake Powell are not alone. According to modeling done in July, Lake Mead is forecast to continue dropping through much of the rest of the year.