Non-native crayfish pose the biggest threat to native fish swimming in the 14 miles of the Fossil Creek restoration project.
Scientists estimate crayfish found their way into Southwest waters several decades ago.
"It appears crayfish have been in Fossil Creek for many years, but they are just now making it to the head waters of the creek," said Allen Haden, Ph.D., a Northern Arizona University aquatic ecologist.
"The crayfish are invasive," he said. "There is no way to deal with their abundance."
Humans should not move crayfish from stream to stream, according to the Arizona Department of Game and Fish.
The hope is that the native fish, perhaps the chubs, will eat them.
"We are pretty certain that the crayfish will have a detrimental effect on the abundance of algae, leaf litter and (insects) available for the native fish community to eat," he said. "They may be able to coexist quite well. We just don't know."
For the next four years, the Fossil Creek project will be monitored.
"I think the public should be aware and be pretty proud of the restoration effort that is going on in Fossil Creek," Haden said. "The restoration of river eco-systems is gaining importance across the globe as we are losing the ecological services those rivers and streams provide."
Most dam removal and retrofit projects are never monitored for success, making Fossil Creek an exception and a valuable source of information for future projects.
The Fossil Creek reclamation project focused on an area that was once home to the Irving and Childs Power Plants.
Built in 1909 and 1915, the power plants diverted the flow of the waters in Fossil Creek to generate power for the copper mines in Jerome.
After the power plants were decommissioned in 2004, a crew of biologists worked around the clock for two weeks to save 2,100 native fish (such as chubs).
Antimyein, a chemical lethal to fish but destroyed by water and sunlight within eight hours, was added to the water to remove all of the non-native fish such as small mouth bass and green sunfish. It did not bother the crayfish.
In June 2005, Fossil Creek was restored from .5 cfs to its original flow of 43 cfs. Since then, the area has been closely monitored to determine its success.
"Restoration is artificial, but (we do it) using the best scientific knowledge we have to reintroduce native populations and hopefully bring them back in abundance," Haden said. "Hopefully, (what we do) will be good for the fish."
For more information, visit http://watershed.nau.edu/fossilcreekproject/.