 Cascades Diversion Dam was a timber crib dam built in 1917 near where the Merced River flows out of Yosemite Valley . Because of its impact on the environment and damage from floods , the dam , originally built to generate hydropower , was decommissioned in 1985 and removed in the 1990s . The U.S. Bureau of Reclamation surveyed the dam site in 1997 and found that the dam was in danger of failure . Classified as a " high hazard " structure , it was originally considered for inclusion on the National Register of Historic Places but was deemed too dangerous to keep . Today , the Merced to Lake McClure is completely free @-@ flowing and unobstructed by any dams . 
