State biologists probing fish kill from Tibble Fork dam reconstruction


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AMERICAN FORK CANYON — A significant amount of sediment that washed into the American Fork River and killed dozens of fish is already starting to dissipate in some areas, but the bigger challenge lies in the months ahead for engineers to keep it from happening again.

An angler discovered the fish kill Monday, prompting a flurry of response from federal, state and county agencies, as well as conservation groups such as Trout Unlimited.

The problem is the U.S. Department of Agriculture's Natural Resources Conservation Service needs to completely drain the aging Tibble Fork Dam in a $7.3 million must-do rehabilitation project designed to extend the life of the 1960s-era dam another 50 years.

Draining it is necessary to raise the structure of the dam by 15 feet, and engineers are now figuring out a design plan to reroute the creek and river that flow into the reservoir's basin.

Dave Brown, state conservation director with the Natural Resources Conservation Service, said a strong rain event could send more debris into the river, acting much like a burn scar after a wildfire.

"Some sediment release was not unexpected, but the extent of this was more than we expected," Brown said.

Thick, black mud despoiled the river as it flowed through several popular campgrounds in American Fork Canyon on Tuesday morning.

Both state wildlife officials and Trout Unlimited leaders said the sludge wiped out fish in a 2-mile stretch of river at its north fork. The area is extremely popular among anglers for German brown and rainbow trout.

"That is 2 miles of one of the best stretches of this river," said Brian Wimmer, president of the Utah County Alpine Anglers chapter of Trout Unlimited.

Wimmer expressed frustration Tuesday that the organization wasn't involved earlier in the planning efforts to drain the lake and coordinate the releases of water.

"This is what Trout Unlimited is all about," he said. "We are the boots on the water. Finding about this the way we did put us back on our heels. "

Mike Slater, regional aquatic biologist with the Utah Division of Wildlife Resources, reported that there were dead fish in the north fork of the American Fork River, but said it does not appear the river's entire aquatic system was wiped out. Macroinvertebrates do not appear to be affected.

Slater, Wimmer and others spent Tuesday in the canyon surveying fish populations and any kills from the sludge. The Utah Department of Environmental Quality also did some sampling to determine if any heavy metals are present in the sludge, but results are not expected for a few days.

Brown said his agency's environmental analysis conducted before the construction project received approval found there were trace quantities of lead in the sediment at Tibble Fork, but they did not exceed federal standards.

As of Tuesday, there were no public restrictions imposed on accessing the river or campgrounds up the canyon.

The Tibble Fork Dam, built in 1966, was constructed for flood control, not water supply.

When its rehabilitation is complete, new features include about an acre-beach area, more parking and greater surface area for fishing and boating.

A buildup of sediment at Tibble Fork was already beginning to compromise the angling and fishing experience, and multiple structures needed to be addressed for safety reasons. Project engineers said sand deposits under the lake's bed posed a risk for liquefaction during an earthquake.

Downstream communities at risk include Cedar Hills, Highland, American Fork and Pleasant Grove.

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Amy Joi O'Donoghue

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