Arapaho Glacier is an alpine glacier in Colorado, located in a cirque southeast of North Arapaho Peak in Roosevelt National Forest, just east of the Continental Divide in the Front Range. Recognized as the state's largest glacier, it is significant not only as a striking high-mountain landform but also because it helps supply water to the city of Boulder. Over time, the glacier has steadily shrunk. With a negative mass balance, it loses more ice than it gains, and during the 20th century it lost more than 52 percent of its surface area, making it an important example of glacier change in Colorado.