Why biologists want to 'reset' this Utah reservoir to help its trout population

An undated photo of Navajo Lake in Kane County. State wildlife biologists say they want to treat the lake with a substance that will kill off fish and then "reset" it a trout fishery.

An undated photo of Navajo Lake in Kane County. State wildlife biologists say they want to treat the lake with a substance that will kill off fish and then "reset" it a trout fishery. (Utah Division of Wildlife Resources)

DUCK CREEK VILLAGE, Kane County — Navajo Lake is a popular spot for anglers to reel in four types of trout species but between drought and the emergence of another fish, all those four species are struggling to survive in the water.

In an effort to change one of those issues, state biologists announced Tuesday they want to use a substance that would kill off most of the fish in the reservoir located off state Route 14 south of Cedar Breaks National Monument between Duck Creek Village and Cedar City. Biologists would eventually repopulate it with trout.

Richard Hepworth, the southern region aquatics manager for the Utah Division of Wildlife Resources, said rainbow, brook, splake and tiger trout in Navajo Lake, which are considered the "preferred" fish species there, are struggling as a result of Utah chub that have outcompeted them in the water. Utah chub now account for over 90% of the fish in the reservoir.

In an effort to keep the area a trout destination, biologists want to cut out the chub. The specific plan calls for the use of rotenone in the reservoir sometime in mid-October. The substance comes from the roots of a tropical plant that's toxic to fish but considered harmless for people, pets or other wildlife when used properly.

Officials said Tuesday they would use it in "extremely low quantities" to avoid any issues to those who recreate at the reservoir and wildlife. But it would help them "reset" the fishery.

The division has used a similar process for some bodies of water across Utah in recent years, including some areas in the High Uintas this month. After fish are killed and cleaned out, state biologists restock the treated body of water with the fish species preferred for the body of water. With the High Uintas, that's the native Colorado River cutthroat trout.

Utah chub is, of course, only half of the issue plaguing trout in Navajo Lake. Due to the drought, low water levels at the reservoir are low enough that trout are impacted by the warmer water that holds less oxygen.

The division increased the limit of trout that people can catch at Navajo Lake on July 28 so people could scoop the fish out before they otherwise would die in the water. The daily limit is currently 16 trout of any size as a result of the change.

But those low levels are also why Hepworth said it could be the best time for the division to treat the water.

"With the low water levels this year due to drought, this treatment to reset the fishery would be much more cost-effective, so we thought it would be good timing," he said in a statement. "We have exhausted all our other tools and efforts to restore the fishery, so this is our last option."

Wildlife officials said Tuesday they plan to have a meeting about the proposal on Sept. 10, at the Duck Creek Village Fire Station, 3620 Mammoth Creek Road, before they will conduct the treatment in October.

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