Some western areas of Rocky Mountain National Park will close from Aug. 25 to 31, including the Colorado River Trail and Grand Ditch, as part of the Poudre Headwaters Project, according to a press release from the park.

Officials will close access to areas on the west side of the park in order to remove non-native fish from the Grand Ditch and other tributaries both upstream and downstream. Once the areas are confirmed to be free of non-native trout, biologists will reintroduce the native greenback cutthroat trout to its original habitat in the headwaters of the Cache la Poudre River, according to the release.

Aquatic biologists with the U.S. Forest Service, in collaboration with Colorado Parks and Wildlife and the U.S. Fish and Wildlife Service, will apply the fish management pesticide rotenone to 14.3 miles of waterways. The chemical is lethal to fish and will eliminate the non-native brook trout that threaten the recovery of the greenback cutthroat.

Water in rotenone-treated areas may appear red, and park officials warn visitors not to drink, eat fish or handle dead fish from these areas. Warning signs will be posted to mark dangerous areas, the release stated.

Despite closures in restoration areas, the park said it would keep the following trails open during the project in the Kawuneeche Valley: East Inlet Trail, North Inlet/Tonohutu Trail, Green Mountain Trail, Coyote Valley Trail, Onahu Trail, Timber Lake Trail, Holzwarth Historic Site and the Harbison Meadows Picnic Area.

In all areas south of the Colorado River Trailhead, fishing will remain open. While the river may appear brown due to treatments upstream, park officials said the water is safe for both humans and fish.