About the Project

The Little Cimarron River forms in the Uncompahgre Wilderness, high on Colorado’s Western Slope. It flows for 25 miles before joining the mainstem Cimarron, which meets the Gunnison River at the Black Canyon of the Gunnison National Park. The Little Cimarron’s upper reaches are prime fish habitat.

The lower reach, however, passes through agricultural land and is de-watered much of the year – a problem the Colorado Water Trust has worked to remedy since 2010. The removal and replacement of the Collier Diversion was proceeded by the Colorado Water Trust’s purchasing a portion of the McKinley Ditch and associated water right. The Trust worked to change the water rights at McKinley Ditch to satisfy the needs of both migrating fish and local ranchers. In 2018, a first-of-its-kind water rights decree in Colorado allowed a “split season” operation of the diversion: Irrigation use now occurs early in the season, while late in the season, when water levels are lower and temperatures are higher, water is turned back to the river.

However, this innovative diversion operation wasn’t enough to restore the Little Cimarron River. The Collier Diversion, an 8-ft-tall by 40-ft-wide concrete structure located 2 miles downstream of the McKinley Ditch, typically diverts all the remaining river flows, rendering the Trust’s instream flow rights meaningless. It also blocks fish passage at all but high spring flows. This project will update the diversion structure to a roughened channel to ensure irrigation diversion is maintained while also providing instream flows and viable fish passage.

This work will open access to 19.5 miles of high-quality fish habitat above Collier Diversion. The end result is a wide and creative range of mechanisms that are restoring the Little Cimarron River, benefiting both the river’s ecology and fish and the community’s agricultural interests.