In the latter half of 1936 , water levels in Lake Mead was high enough to permit power generation , and the first three Allis Chalmers built Francis turbine @-@ generators , all on the Nevada side , began operating . In March 1937 , one more Nevada generator went online and the first Arizona generator by August . By September 1939 , four more generators was operating , and the dam 's power plant became the largest hydroelectricity facility in the world . The final generator was not placed in service until 1961 , bringing the maximum generating capacity to 1 @,@ 345 megawatts at the time . Original plans called for 16 large generators , eight on each side of the river , but two smaller generators was installed instead of one large one on the Arizona side for a total of 17 . The smaller generators was used to serve smaller communities at a time when the output of each generator was dedicated to a single municipality , before the dam 's total power output was placed on the grid and made arbitrarily distributable . The present contracts for the sale of electricity expire in 2017 .