Lake Powell, the second major reservoir on the Colorado River, is also at historic low levels. 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. 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.