Picacho Reservoir is just 11 miles (18 km) south of Coolidge in central Arizona. The reservoir was built in the 1920s as part of the San Carlos Irrigation Project. The reservoir's original purpose was water storage and flow regulation for the Florence-Casa Grande and Casa Grande Canals. The lake's design capacity was 24,500 acre feet (30,200,000 m³) of water, with a surface area of over 2 square miles (5.2 km²). Over the years, siltation and vegetation have reduced the capacity and surface area, so that much of the reservoir is a shallow marsh with extensive stands of cattails and rushes.