Western Division Project Spotlight: Rio Costilla Restoration Project for Rio Grande Cutthroat Trout

Rio Grande Cutthroat Trout (RGCT) is the southernmost subspecies of Cutthroat Trout and is native to portions of New Mexico and Colorado. Only a fraction of RGCT historic range is currently occupied primarily due to competition with species like Brook Trout and Brown Trout and hybridization with Rainbow Trout.  The Rio Costilla restoration project was developed to expand RGCT range by removing nonnative fishes with piscicide and restoring RGCT to 120 miles of stream, 10 lakes, and a 300-acre reservoir (Figures 1 and 2). This ambitious project required the coordination of several agencies and stakeholders and is the largest native fish restoration project in the country. The first piscicide treatment within the basin occurred in the late 1990s, but the majority of work for this large-scale project began in 2002 and concluded in 2022. Temporary fish barriers were constructed throughout the project area to block the upstream movement of nonnative fishes and removed as areas were restored. The permanent fish barrier at the downstream end of the project area was constructed in 2016 (Figure 3). After a final piscicide treatment in the spring of 2022, the Rio Costilla and its tributaries were stocked with Rio Grande Cutthroat Trout. Other native fishes such as Rio Grande Chub and Rio Grande Sucker will also be stocked in the project area in 2023. The project was a collaborative effect between the New Mexico Department of Game and Fish, Turner Enterprises Inc., the U.S. Forest Service, Colorado Parks and Wildlife, The U.S. Fish and Wildlife Service, and Trout Unlimited.

Figure 1. Map of the Rio Costilla project area.

Figure 2. Tributary stream flowing into the Costilla Reservoir.

Figure 3. Permanent fish barrier on the Rio Costilla.