Rocky Mountain National Park will close the Colorado River Trail, the Grand Ditch, and everything in between for a week starting Monday. The reason for the Kawuneeche Valley closure is a small green fish that Colorado nearly lost forever, and it is worth celebrating, not grumbling about.
If you have west-side plans for next week, check them now. Beginning Monday, August 24, Rocky Mountain National Park will close all trails and terrain in the northern Kawuneeche Valley through Sunday, August 30. That includes the Colorado River Trail, the Grand Ditch, and every trail inside the project zone west of the river.
The closure notice mentions “the Poudre Headwaters Project,” which sounds like paperwork. It is actually one of the most ambitious wildlife recovery efforts in the state, and next week is the part where crews wade in and do the work.
What the Kawuneeche Valley closure covers, and what stays open
Here is the short version from the park’s August 5 announcement:
- Closed August 24 to 30: the Colorado River Trail, the Grand Ditch, and all areas and trails within the project zone. The closure applies to all uses, so no hiking, fishing, or off-trail travel inside the boundary.
- Still open on the west side: the East Inlet, North Inlet/Tonahutu, Green Mountain, Coyote Valley, Onahu, and Timber Lake trails, plus the Holzwarth Historic Site and the Harbison Meadows Picnic Area.
- Fishing stays open along the Colorado River south of the Colorado River Trailhead, including near Holzwarth and Coyote Valley.
Trail Ridge Road is not part of the closure, so driving over the top and stopping at the west-side pullouts is unaffected.
What crews are actually doing in there
For one week, biologists led by the U.S. Forest Service, working with the park, Colorado Parks and Wildlife, and the U.S. Fish and Wildlife Service, will treat the 14.3-mile Grand Ditch system and its connected tributaries with rotenone, a fish-killing compound, to remove brook trout and other non-native fish. A first round of treatment covered the same ground in August 2025. Once the non-natives are gone, greenback cutthroat trout will be reintroduced to the headwaters of the Cache la Poudre River, water they have not occupied in recorded history.
If “putting poison in a river” makes you flinch, that is a reasonable first reaction. Rotenone is a plant-derived compound registered with the EPA that affects gill-breathing animals, and agencies like CPW have used it in fisheries work for decades because it breaks down quickly and does not pose a meaningful risk to people, dogs, or the elk and moose that make the Kawuneeche famous. The closure exists so crews can work and so nobody wanders through an active treatment area.
Brook trout are the villain of this story only by accident. They are a beloved sportfish, but in these small headwater streams they outcompete young greenbacks for food and space. You cannot restore the native fish while the competition is still in the water. Remove them completely, or the project fails.
Free: Complete Colorado 14ers Planner
Every peak. Every trailhead. Every detail: in one spreadsheet.
- All 58 peaks ranked beginner to expert
- Safety notes and seasonal windows for each
- Route difficulty, mileage, and prep tips
The fish worth closing a valley for
The greenback cutthroat trout is Colorado’s state fish, and for decades biologists believed it was extinct. Then in 2012, researchers confirmed that a single wild population had survived in Bear Creek, a few miles of small stream on the edge of Colorado Springs. The strangest part: those fish were probably carried there in the late 1800s to stock a tourist fishing operation, far from their native South Platte waters. A century later, that accident of history turned out to be the species’ lifeline.
Every greenback swimming today descends from that one creek. Since the rediscovery, CPW and its partners have been carefully breeding the fish and returning them to stream after stream along the Front Range.
The Poudre Headwaters Project is the biggest swing yet. Colorado Trout Unlimited calls it the largest native trout restoration effort in state history, with a goal of nearly 40 miles of connected streams and multiple lakes, including Long Draw Reservoir, as a permanent stronghold for the species. The full effort is expected to take a decade or more. A week of closed trails next week buys a piece of that.
Planning a west-side trip anyway
The Kawuneeche Valley is my favorite corner of the park in late August. The crowds thin out, the elk start getting loud, and the light turns gold by late afternoon. One closed corridor does not change that.
- The East Inlet and North Inlet/Tonahutu trails out of Grand Lake stay open all week, and both are better hikes than the Colorado River Trail anyway.
- Coyote Valley is the easy, flat, family option, and it stays open along with the fishing access there.
- You still need a timed entry reservation to enter the park during peak hours, closure or no closure.
- Check the park’s conditions page before you drive up. Closure boundaries can shift, and late August weather has opinions of its own.
Respect the closure signs, even where the trail looks empty and inviting. The people on the other side of them are trying to hand your grandkids a river full of native trout.
Featured photo and trout photo courtesy of the U.S. Forest Service (stream photo by Jen Williams, USFS). Closure map courtesy of the National Park Service. Reporting from the National Park Service, the U.S. Forest Service, Colorado Trout Unlimited, and The Colorado Sun. For current conditions, check the RMNP conditions page.
RECENT MOUNTAIN NEWS
