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Small Tonto Forest fish barrier could have large impact on ecology

TONTO NATIONAL FOREST – After driving past the end of the paved entrance road, over two stomach-churning miles of rugged terrain, and then hiking two more miles across slippery boulders, there is a particularly rocky section of Lime Creek.

It's an arduous journey to reach this point, roughly three miles upstream of the Horseshoe Reservoir – but one that's still too easy for many non-native aquatic species that may threaten the ecological balance here in the Tonto National Forest.

To preserve this balance, Salt River Project began construction this week on a barrier between two rocky outcroppings in a remote part of the forest. The dam, which is expected to cost about $125,000, will prevent non-native species from traveling farther upstream.

"The Forest Service is extremely excited about this project," said Andre Silva, a wildlife and fishery biologist for the Tonto Forest.

"There are no non-native species that are known to live above where the barrier will be built," said Silva, "so once it's built, there will be four miles of aquatic habitat that's pristine."

He said crayfish, mosquitofish and bullfrogs are all examples of aggressive and non-native wildlife that the barrier would prevent from further infiltrating native species' habitat.

Several native species – including the longfin dace, Sonoran desert toad and Gila topminnow – stand to benefit from the reduced competition if the barrier works as designed.

SRP is building the barrier as part of a habitat conservation plan approved by the U.S. Fish and Wildlife Service in 2008 to offset damages caused by its ongoing operation of Horseshoe and Bartlett reservoirs.

The project is funded privately by an alliance between SRP and the city of Phoenix.

The Lime Creek barrier is just the latest project in that plan; SRP is also involved in setting up a 150-acre conservation easement for willow flycatchers near Fort Thomas and upgrading the facilities at the Bubbling Ponds fish hatchery outside Sedona.

"The Forest Service highly values partnerships such as this," Silva said. "SRP stepped up and did an excellent job, spearheading a project that will benefit this forest and the native species here for years to come."

On Tuesday, the sound of a helicopter could be heard echoing across the sparse, mountainous landscape as it carried construction materials from the SRP field house near the reservoir to the barrier site.

Construction began Monday and is expected to last from 10 to 14 days, barring any rainstorms that could delay the project. A team of laborers will camp near the site until it's completed.

The finished barrier will be approximately 5 feet tall and 20 feet long, blocking Lime Creek as it flows between two steep embankments of granite.

Once the materials are in place inside the narrow gap, a temporary diversion dam will be built and forms will be constructed for the permanent dam. A kind of concrete specially formulated to withstand conditions in the forest will be poured for the barrier.

"Because the bedrock narrows the stream so much, it makes our job easier," said Chuck Paradzick, an SRP environmental scientist supervising the project.

"What we're trying to do is minimize our impact while maximizing preservation."

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Click image to enlarge

Grant Martin/Cronkite News Service

Project manager Chuck Paradzick and Forest Service biologist Andre Silva examine netting placed just upstream of the dam’s construction.

Key facts

  • In the Tonto National Forest, there are 21 animals listed among federal and state endangered or threatened species.
  • At nearly 3 million acres, the Tonto National Forest is the largest in Arizona and the fifth-largest in the nation.
  • Approximately 5.8 million people visit the Tonto National Forest annually.
  • SRP is the largest provider of water and power to the greater Phoenix metropolitan area.