Ice from Lake Erie flows over the falls and jams up the gorge below. An ice bridge is an accumulation of ice that has frozen solid from shore to shore, under which the river still flows. In the past, the American Falls and Bridal Veil Falls were frequently reduced to a trickle when ice jammed in the American Rapids, and a few times both falls completely froze over. Since 1964, the installation of the ice boom, a barrier laid across Lake Erie, has slowed the amount of ice flowing down the falls.