Mill Creek turns pink to reclaim habitat for native trout

Wildlife experts are turning Mill Creek pink this week — on purpose.

Officials and volunteers from the state Division of Wildlife Resources, the U.S. Forest Service and other partners will "taint" a portion of the creek in Millcreek Canyon with a purplish cleansing agent this week.

The agent — potassium permanganate — will neutralize a chemical compound the DWR is using upstream to clear the creek of non-native fish species.

The piscicide, called rotenone, will be used to treat Mill Creek from Elbow Fork down to the mouth of the canyon. At that point, DWR will mix in potassium permanganate to prevent the poison from moving downstream.

It will turn part of the stream, a stretch of about one-third to one-half of a mile, into a purple or pinkish color for a couple of days this week, but the colored water is harmless, said Mike Slater, a regional aquatics manager for DWR. Potassium permanganate is a purifying agent commonly used at water treatment plants, he said.

"This makes sure we don't have any impact on those fish outside the canyon," Slater said.

Rotenone is only toxic to species with gills except in very large doses. According to DWR, a human would have to drink 40,000 gallons of the treated creek water within 24 hours to receive a toxic dose. A bird would have to eat 40 pounds of the deceased fish in 24 hours before it got a lethal dose.

After the dead fish are removed, DWR will release native Bonneville cutthroat trout and other native species into the creek this October.

"I don't like removing fish any more than anyone else, but it is a necessity," Slater said, explaining non-native species tend to outcompete native species, and non-native trout breed with Bonneville cutthroat, creating hybrids.

Native trout released last fall in the uppermost portions of the creek, above Elbow Fork, are nearing six inches in length and can be found throughout the upper Mill Creek system, Slater said. By this time next year, the area will be ready for anglers to return, he said, and the fish should begin to reproduce the year after that.

"They're doing exactly what we had hoped," Slater said. "By next year … it will be a really neat opportunity for people to come interact with a truly native species community."

The Mill Creek restoration, which is scheduled to be completed in September 2016, represents a unique opportunity in Utah, Slater said. Because Mill Creek isn't a source of drinking water, DWR had the option to treat it for mass removal of non-native fish — a strategy that will create a purely native population for anglers and wildlife enthusiasts.

"We want to provide lots of different opportunities for the public," he said. "One size doesn't fit all."

epenrod@sltrib.com

@EmaPen