CEDAR CITY — Navajo Lake will be treated later this fall to rid it of undesirable non-game fish, wildlife officials say.
Richard Hepworth, aquatics program manager for Utah Division of Wildlife Resources, told the Iron County Commission at its regular meeting on Monday that sometime in September, the water will be treated with rotenone, a natural piscicide designed to kill all the fish in the lake.
Hepworth said that approximately 94% of the biomass of fish currently in Navajo Lake is made up of Utah chubs, “which doesn’t leave a lot of room for the trout that most of our fishermen really want.”
Hepworth told Cedar City News after the meeting that even though trout were stocked in the lake this spring, they didn’t appear to last very long.
“We put them in there and those trout just can’t compete,” he said. “We netted it, and boy, it’s in sad shape. It really is. There’s not much there right now. We want to get this back to what it can be.”
The last rotenone treatment at Navajo Lake took place in 1997, he added.
“So we got a little bit over 20 years out of that project,” he said, adding that he hopes this year’s treatment will last as long as 30 years, thanks to improved complement formulas and strategies.
Treating fisheries with rotenone is not a new concept, he said, adding that the technique has been utilized periodically over the past several decades.
“It’s just one of those tools that we use a lot in fisheries management,” Hepworth said.
Although highly toxic to fish, rotenone is relatively harmless to humans and other warm-blooded animals.
“Things like deer, elk, coyotes and birds are going to come in and eat the fish,” Hepworth said. They’re going to drink the water. It’s safe for all those things. We’ve never had an instance, using this for probably nearly 100 years in Utah, where we’ve had an issue with it.”
“The biggest risk is to those of us putting it out,” he added. “Because it’s a very fine powder, just like any other very fine powder, it’s just not good for getting in your lungs. So we’ve got to be careful. But from an environmental impact, it’s very safe.”
Although it can be neutralized by applying an agent such as potassium permanganate, rotenone also naturally detoxifies when it passes into the soil.
“We’ve done Navajo, like four or five times now in history and have never had to do any detox there,” Hepworth said.
Some of the major Southern Utah waterways that have undergone periodic rotenone treatments include Panguitch Lake, Kolob Reservoir and Gunlock Reservoir.
“We’ve done lots of other small ones,” Hepworth said. “The Virgin River is getting done right now. Well, it was done last week, and it will be done again next week.”
Hepworth told the Iron County Commission that the DWR is taking advantage of the current drought situation by scheduling the treatment when the lake’s water level is low, thereby reducing the amount of rotenone needed. The estimated cost savings is approximately $60,000 to $80,000, he added.
Noting that Navajo Lake is located within Kane County, Hepworth said he already visited the Kane County Commission last week to give them essentially the same information
“September is the time frame we’re looking at,” he said. “We’ll try and do it after Labor Day to make sure to do it at a time when there’s not a lot of people in the area.”
“We can restock first thing in the spring and have a better fishery for the next few years,” Hepworth said.
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