Walking along the banks of Mill Creek, a stream running out of Millcreek Canyon, one won’t see the typical clear water flowing downstream this week.
On Sept. 1 and 2, the water appeared a deep blood red.
The Utah Division of Wildlife Resources — in conjunction with the U.S. Forest Service, U.S. Fish and Wildlife, and Trout Unlimited — are conducting a treatment on a portion of the creek in the Uinta-Wasatch-Cache National Forest.
The division poured Rotenone — a natural substance from the roots of a tropical bean plant — into the water to help restore native Bonneville cutthroat trout.
“These treatments will help to create a population of cutthroat trout that will contribute to the conservation of native cutthroat trout species and prevent them from being listed under the Endangered Species Act,” said Central Region aquatics manager Chris Crockett.
But not all Utahn’s agree with the division’s policies — some oppose the use of the chemicals, citing prior studies linking them to Parkinson’s disease.
Why wildlife officials stand by the process
This isn’t the first time the Division of Wildlife resources has treated Mill Creek.
Nearly a decade ago, biologists underwent a similar operation for a 10-mile stretch of the creek to remove nonnative rainbow and brown trout. Previously, someone illegally introduced brook trout within the canyon, “causing threats to native fish species in the area,” the divisions press release read.
Now, an illegally-introduced brook trout have invaded the waters — and wildlife experts are hoping to save native species.
“An angler reported catching a brook trout in Mill Creek a few years ago, and we later confirmed them in parts of the creek,” said Crockett. “We know these fish were illegally introduced because even before the previous treatments in 2013-2016, there were no brook trout in Mill Creek.”
In Utah, it is illegal to transport live fish or to introduce them into a new location. It could result in a class A misdemeanor, which comes with possible jail time and fines.
“The selfish and illegal actions of an individual are now endangering native trout and costing anglers valuable resources that could be used elsewhere,” Crockett said.
Habitat loss, spawning with nonnative trout and competition from non-native trout have caused dramatic declines in native cutthroat trout populations across the West, leading to concerns about the species’ future.
The division reported the fill treatment will include 3 miles of the creek, from Church Fork to the I-215 bridge crossing. A series of two to three treatments is the standard protocol — the second Mill Creek treatment will likely occur late in September or will be scheduled for the fall of 2027.
“We will not manage for illegally-introduced species, so any future illegal fish introductions in this area will result in similar removal efforts,” sportfish coordinator Trina Hedrick said.
What is Rotenone — and why are some against it?
The Division of Wildlife Resources claims there is no risk to exposure to rotenone in the quantities used in water bodies throughout the state.
Rotenone is a respiratory toxin to fish, “but it is not dangerous to people, pets or other wildlife, especially in the extremely low quantities that biologists use to treat streams and lakes,” the division published on its website.
Advocates online have openly shared their disapproval of the process.
One post on Instagram — with over 2,600 likes in only one day — states: “This isn’t for the wellbeing of native fish; this is for people to have more unique fishing opportunities to catch native trout. This is for the state of Utah to sell more fishing licenses.
“That poison is being dumped into the water supply simply as an economic investment,” the post continued.
A 2025 study has linked continued exposure of the pesticide to Parkinson’s disease, though the division claims the small doses used are incompatible with large, continuous doses in the study.
Hedrick said the state is attempting to restore native cutthroat trout to key places around the state, and “other competing trout species aren’t compatible in these identified conservation areas.”
In an effort to save native fish, biologists safely catch as many cutthroat trout as possible before the treatment begins. Those fish are held on-site and released back into the creek once the water is deemed safe for the fish.
“The salvaged Bonneville cutthroat trout and fish upstream of the treatment site will quickly repopulate the treated area,” the division said.
In the meantime, the Division of Wildlife Resources encourages the public and their pets to stay out of treatment areas.
“Anglers will encounter slightly reduced cutthroat trout numbers after the treatment as the fish spread out, but nearby upstream areas will not be impacted,” Central Region sportfish project leader Mike Slater said. “Anglers wanting to target cutthroat trout in the area can go above Church Fork to take advantage of higher fish numbers and great small-stream fishing for native cutthroat trout.”
