APS
Stehr Lake covered nearly 28 miles and was built in 1908 by constructing two earth-filled dams to create a reservoir. Diverted water from Fossil Creek was brought here through a series of flumes and pipes, after first passing through the Irving plant. The water then continued to the Childs Surge Tank before heading into the Childs Powerhouse to generate electricity. Stehr Lake provided a reservoir to run the Childs Plant when repairs and maintenance activities shut off the water from the flume. The lake held sufficient water to run the plant for more than three days.

Wiki
Between the Irving and Childs plants, the creek water exited the flume and tunnels and entered an artificial reservoir, Stehr Lake. The lake provided a backup water supply for the Childs plant when the flume system above the lake was shut down for maintenance. The lake held enough water to run the plant normally for 3.5 days.

Named for Frederick W. Stehr, treasurer of the Arizona Power Company.