Frequently asked questions about the Mill Creek restoration project
Many people have had questions about the fish-removal and restoration work planned for Mill Creek. Here are the most common questions and answers:
Why is it important to restore Bonneville cutthroat trout?
There are three primary subspecies of cutthroat trout native to Utah. By the middle of the twentieth century, all three subspecies — Bonneville, Colorado River and Yellowstone — were thought to be extinct. When a few isolated populations were discovered in Utah in the 1970s, biologists began an in-depth search, and cutthroat recovery became a priority across the West.
Today, after an aggressive, coordinated recovery effort by a multi-agency conservation team, there are now Bonneville cutthroat trout populations that occupy nearly 2,500 miles of stream in Utah and bordering states. Restoring Mill Creek's Bonneville cutthroat population will be another important step in the overall recovery of this species.
What fish species are currently in Mill Creek?
Mill Creek has a mix of fish species. There are cutthroat, brown and rainbow trout as well as cutthroat-rainbow hybrids. If those fish remain in the creek, they will breed with the pure-strain Bonneville cutthroats and thwart the species-restoration effort.
How will those fish species be removed?
Project partners will use rotenone to remove the fish currently in Mill Creek.
What is rotenone?
Rotenone is a natural substance that comes from the roots of a tropical plant in the bean family. It is a piscicide (substance poisonous to fish). Rotenone makes it impossible for fish to use the oxygen absorbed in the blood. The U.S. Environmental Protection Agency has approved the use of rotenone to control and sample fish populations in lakes, ponds and streams. Utah has used it many times to control invasive species and to restore native and threatened species.
Is rotenone dangerous to people, pets or wildlife?
No. The highest allowable rotenone treatment rate is .25 mg per liter of water. At that concentration, a 132-pound person would have to drink 40,000 gallons of treated water in a 24-hour period to receive a lethal dose. Likewise, a 0.25-pound bird would have to drink 100 quarts of treated water — or eat more than 40 pounds of fish and invertebrates — within 24 hours to receive a lethal dose.
Is there a relationship between rotenone and Parkinson's disease?
In 2000, a rotenone study was conducted in an attempt to produce symptoms similar to those of Parkinson's disease (PD). Rotenone was injected directly into the jugular veins of rats for a five-week period, and under those conditions, it did produce some PD-like symptoms. The study does not suggest that rotenone exposure is responsible for PD in humans, but does support the belief that chronic exposure to high concentrations of environmental toxins can increase the likelihood of the disease.
Does rotenone affect all aquatic animals in the same way?
No. Fish and other gilled organisms are more susceptible to rotenone. All animals have natural enzymes in the digestive tract that neutralize rotenone.
Is rotenone a groundwater contaminant?
No. The ability of rotenone to move through soil is low to slight (less than one inch in most soils). Wells and groundwater will not be affected. Monitoring studies have shown that groundwater in adjacent areas has not been affected.
How is rotenone neutralized?
To neutralize the effects of rotenone, project partners will use potassium permanganate, an oxidizing agent. Potassium permanganate breaks down into potassium, manganese and water. Both potassium and manganese are common in nature and have no harmful environmental effects at the concentrations used in the neutralization processes. Potassium permanganate will turn the water a purple color until it is diluted while traveling downstream.
Who will perform the rotenone treatment and neutralization?
Personnel from multiple agencies will conduct the treatment, which will be regulated by the Utah Department of Environmental Quality. All personnel who dispense rotenone are required by law to have a certified Pesticide Applicators Permit.
Will there be any noticeable effects of the rotenone treatment?
All of the fish removal will occur in the canyon, and there may be a few noticeable effects:
Where can I learn more about rotenone?
For more information on the use of rotenone to control fish populations, see the Rotenone Stewardship Program.
What other central Utah waterbodies have been treated with rotenone to remove fish?
The following central Utah fisheries have been treated with rotenone in recent decades:
What are the project timelines and when will the Bonneville cutthroat trout be stocked in Mill Creek?
Here's a quick look at proposed project timelines and restocking efforts:
Each of the three sections of Mill Creek will be treated in two consecutive years (during the fall). Immediately following the second treatment of each section, native Bonneville cutthroat trout will be restocked in that section of stream. Those trout will come from Little Dell Reservoir, which is a wild brood source of Bonneville cutthroat trout for Wasatch Front waterbodies.
What are the plans for habitat restoration and enhancement?
Visit the U.S. Forest Service website for detailed information on their work to restore the watershed, enhance habitat and maintain safe public access in Mill Creek Canyon.
Where can I learn more about this project or ask some questions?
If you want to comment on this project, please email us at