By VERNON ROBISON
Moapa Valley Progress
If Moapa residents see a lot of dead fish or a purple residue floating downstream on the waters of the Muddy River this winter, they should not be alarmed; everything is going exactly as planned. That was the general message of a presentation given to the public at the Moapa Town Advisory Board (MTAB) meeting held on Tuesday, July 26.
The Nevada Department of Wildlife (NDOW) in coordination with the U.S. Fish and Wildlife Service, is planning an eradication of invasive fish species in a stretch of the upper Muddy River this fall using a chemical known as Rotenone.
In the presentation, NDOW specialist Amos Rehm explained that Rotenone is an odorless, colorless substance, derived from a South American legume. It is commonly used in streams to eradicate non-native species that are threatening the balance of the habitat. When released into the stream at sufficient levels it will kill off all the fish and insect life in the stream, Rehm said.
But it is harmless to humans and other animals, he said. “Rotenone is easily metabolized by mammals,” Rehm explained. “So it is non-toxic to animals and people. While it is classified as a poison, it is one of the safest ones out there.”
In recent years, it had been observed that the Muddy River was overrun by the Blue Tilapia and a multitude of other invasive fish species. The Blue Tilapia, a North African fish, was first reported in the Muddy River in 1991. Since that time it has quickly expanded up and down the river and has wreaked havoc on the natural balance of the Muddy River ecosystem, Rehm said. It is especially a problem because it competes and preys upon native fishes, including the endangered Moapa dace, he said.
Rehm explained that the Rotenone application is carefully contained and monitored. It is targeted to only affect a single limited segment of the river at any given time. That segment is delineated on the downstream end by a fish barrier of some sort, such as a diversion dam or other structure in the river. Downstream of that barrier another chemical agent, potassium permanganate, is added to neutralize the poison. This chemical is a commonly used water purifier and keeps the Rodenone from travelling further downstream bringing unwanted effects, he said.
But the introduction of that neutralizing agent also causes a reaction which results in turning the river water a bright purple color, Rehm said. While this substance is harmless, and breaks down in a short time, it can be alarming to people who don’t know what is going on, he said.
Rehm said that introducing Rotenone into the stream was found to be the most effective way to deal with the non-native species problem.
The process had seen success in previous applications to the upper reaches of the stream, he said. In those reaches, located far up in the Warm Springs area, the procedure had successfully eradicated all of the tilapia from the stream in those areas.
Strategic application of the chemical only in segments of the stream where the dace was not yet present, had kept the dace population unharmed by the chemical, he added.
That application had concluded just last winter and the agencies are looking to expand further downstream this winter, into the area between the Moapa Indian Reservation and the barrier just above Hidden Valley.
“We would like to eventually take this the whole way down to Wells Siting if we can get around to it,” Rehm said.
MTAB member Ryan Udall asked if there had been any negative impacts from the previous applications.
Rehm responded that they had learned that the river’s flow was much faster than expected. In a slower river, the purple color tends to dissipate in a shorter distance, he said.
“I did not think that the purple would come down as far as it did,” he said. “At least one or two people called in and noticed that. And because (the stream) is so swift, a few of the dead fish floated all the way down and got caught on the grates at Wells Siting. So Scott Millington (of Muddy Valley Irrigation Company) was asking why all the dead fish.”
Other than that, there had been no issues with implementation and no issues with public outcry, Rehm said.
“Everyone seemed okay with it and were understanding and at least weren’t angry about it,” he added.
But MTAB member Jamie Shakespear suggested that the reason that there was no previous input from the public might have been because people hadn’t been told about it.
“Was there any notice given to people in Moapa that you were doing this?” she asked. “I don’t think I remember ever hearing that this was going to be happening.”
Rehm said that this was the purpose of his presentation; to let people know about the upcoming portion of the project, which would approach closer to private property than before.
“I think that NDOW typically hasn’t engaged as much of the public as it should,” Rehm said. “That is why I am coming here to make sure that we do.”
Rehm pointed out that all of the previous work done on the upper-most reaches had been done on public entity-owned land including federal and SNWA-held property. Now that the project is coming down closer to Moapa, he wanted to cover all the bases and let everyone know what was happening, he said.
“It may have been wiser to do this presentation last year before we started,” Rehm admitted. “But I was new to the project and just trying to get things up and running.”
Rehm said that the work on the Muddy River is planned as a three year project funded by a grant obtained by the U.S. Fish and Wildlife Service.
