The gates of the Coon Rapids Dam changed over the years to keep up with the flow of the Mississippi River. Built in 1913 to generate electric power for a proposed trolley line, the dam used twenty-eight Tainter gates from 1913 to 1995 to control the river's flow. Each curved metal gate pivoted on a large pin, and raising a gate by hand required 100 turns of a crank to lift it only one inch. When the Tainter gates could no longer operate effectively, inflatable rubber dam sections were installed and completed in 1997, making the Coon Rapids Dam one of the largest rubber dams in North America. Harsh Minnesota winters created challenges for the rubber dams, and in 2015 hydraulic steel crest gates replaced them. These gates measure between 67 and 97 feet long, 8 feet high, and weigh between 32 and 45 tons. Besides improving water level control, the steel crest gates help prevent the migration of Asian carp, an invasive fish species that threatens the Mississippi's headwaters ecosystem.