The Greenback Cutthroat Trout, Oncorhynchus clarkii somias, was adopted as the official state fish on March 15, 1994, by an act of the General Assembly. The Rainbow Trout was considered the state fish from 1954 until 1994 but was never officially adopted. The Greenback Cutthroat Trout was at one time indigenous to many small creeks, streams and rivers throughout most of Colorado. As mining and human occupation expanded across the state, the greenback easily succumbed to pollution from mine tailings in the state's streams and to competition from other species of trout introduced to Colorado waters.
The demise was so complete that up until the late 1980s biologists feared the extinction of this native fish. However, researchers in the early 1990s discovered several small populations of the greenback in a few remote streams in Rocky Mountain National Park. Colorado Division of Wildlife and National Park personnel took immediate steps to protect and propagate the greenback. Plans have been made to reintroduce this colorful fish to other waters within the state which are suitable for its repopulation.