San Carlos Lake was formed by the construction of the Coolidge Dam and is rimmed by 158 miles of shoreline. The lake is located within the 3,000-square-mile San Carlos Apache Indian Reservation, and is thus subject to tribal regulations.
After it was built, the reservoir filled gradually. Because of irrigation needs, the water level at the lake sometimes is low enough to kill its self-sustaining fish, but during wet years, the water can overtop Coolidge Dam. Since construction of the dam, the lake has been nearly empty at least 20 times, and has been full only three times.