Painted Rock Dam - Painted Rock Reservoir

The Painted Rock Reservoir is an artificial reservoir impounded by the Painted Rock Dam. The reservoir, with a maximum storage capacity of 2,491,700 acre feet (3.0735×109 m3), has the potential to be the second largest reservoir completely within the borders of the state of Arizona, but because the Gila River and its main tributary, the Salt River, are generally almost always completely diverted for irrigation and municipal water use for Phoenix, the lake is often dry.

In 2005, heavy runoff filled the reservoir to record levels, swelling the lake to become the second largest by area in the state of Arizona, trailing only Theodore Roosevelt Lake. However, extremely high levels of pesticides, particularly the now-banned DDT, had built up in the farmlands upstream from the reservoir in the decades prior and accumulated in the lake during the flood. The extreme toxicity of the lake rendered it unsuitable for recreational uses and public access to both the lake and the dam was restricted. Similar runoff had filled the lake previously in 1993 and 1980, and in each instance the lake persisted only a few months before emptying due to losses through evaporation, downstream releases, and infiltration.