 The reservoir did not fill completely until spring 1973, when it flowed over the spillway for the first time.Also in 1973, the Bureau of Reclamation also began planning for a hydroelectric power plant at Navajo, which had not been included in the original design of the dam.Construction began in 1976, but was halted when the National Wildlife Federation sued, citing that fluctuating power releases into the San Juan River could cause environmental damage.