Biologists with Colorado Parks and Wildlife (CPW) are closing and treating a section of water within Rocky Mountain National Park to restore native greenback cutthroat trout.
The Grand Ditch—a water diversion project that moves water from the Colorado River drainage to the eastern side of the Continental Divide—will be treated in its entirety, along with all its tributaries within the Park. That will remove all nonnative fish from the watershed, allowing biologists to then plant native greenback cutthroat trout in their historical range. This project will, in effect, restore the headwaters of the Cache la Poudre River to a cutthroat fishery.
Biologists will use rotenone, a piscicide that’s only poisonous to fish, to treat the Grand Ditch and its tributaries. Rotenone is widely used in conservation and restoration projects since it has a negligible impact on aquatic insect life, instead only removing fish from the river system. Native trout can then be quickly reintroduced, bypassing the cost and time investment of mechanical removal of nonnative fish.
The project will take place during the last week of August, and a section of the Park will be closed while the treatment runs its course. The entire Grand Ditch area is scheduled for closure, along with the full Colorado River Trail up to La Poudre Pass.
While some anglers may get upset at losing an option to chase brook trout, or other nonnative trout in this areas, most cutthroat restoration projects only aim to restore native fish to a small fraction of their historical range. Other opportunities to catch brook, brown, and rainbow trout will still exist, in part because most watersheds don’t have the water quality necessary to support cutthroat trout through their entire reaches. Habitat destruction, water diversions, and warming stream temperatures all combine to push cutthroat higher in these systems, where the fish were historically found in abundance.