Colorado is in its first year of responding to a zebra mussel infestation in a big river, the Colorado River. State staff say they have what they need to handle the high-priority needs — they just need their funding to stay off the chopping block.
The fast-reproducing mussels, or their microscopic stage called veligers, were first detected in Colorado in 2022. Since then, the state’s aquatic nuisance species team and its partners have been working to monitor water, decontaminate boats, and educate the public to keep the mussels from spreading. That effort logged a serious failure this summer when state staff detected adult zebra mussels in the Colorado River, where treatment options are limited.
“We’re continuing to sample the Colorado from below the Granby Dam all the way out to the [Utah-Colorado] state line,” said Robert Walters, who manages the invasive species program for Colorado Parks and Wildlife.
Adult zebra mussels, about the size of a thumbnail with a zebra-striped shell, reproduce quickly and can clog up pipes, valves and parts of dams, costing millions of dollars to remove. They also suck up nutrients, out-eating other native aquatic species, and their razor sharp shells cause headaches for beachgoers.
The state’s first adult zebra mussel showed up in Highline Reservoir near Grand Junction in 2022. But even after the lake was drained and treated, the mussels appeared again.
Then this year in July, the mussels showed up in a private reservoir in Eagle County near the Colorado River. And in September, specialists found adult zebra mussels in a stretch of the Colorado River itself.
Colorado has been working to keep these invasive species out of its waters since 2007, when a task force was created to coordinate management efforts.
In 2008, Colorado approved a law that makes it illegal to possess, import, export, transport, release or cause an aquatic nuisance species to be released.
Now, the program completes over 450,000 inspections each year, according to Colorado Parks and Wildlife’s website. The teams have intercepted 281 boats with zebra or quagga mussels attached.
But their treatment options are limited on the Colorado River. CPW does not intend to treat the main stem of the Colorado River due to multiple factors, including risk to native fish populations and critical habitat, the length of the potential treatment area and complex canal systems, the agency said in a mid-September news release.
The goal continues to be educating the public — including lawmakers who are scheduled to hear an update on the zebra mussel issue during the Oct. 29 Water Resources and Agriculture Review Committee meeting.
“What I think that we really need to help us more effectively tackle this issue is a higher level of public awareness,” Walters said.
The first year of infestations
For invasive species teams, the first year involves a lot of monitoring, according to Heidi McMaster, the invasive species coordinator for the U.S. Bureau of Reclamation.
She’d know: She has helped Reclamation with its response to invasive species, like quagga mussels.
Quagga mussels were discovered in Lake Mead, Lake Mojave and Lake Havasu on the Colorado River in January 2007. The mussels were later confirmed in Lake Powell in 2013, according to the Bureau of Reclamation.
Colorado River water from Colorado’s mountains eventually collects in Lake Powell before flowing through the Grand Canyon to downstream states, Lake Mead and Mexico.
“I would think that the first response is probably panic, especially if people are not prepared for it,” McMaster said. “Once that initial panic wears off, it is tapping into the existing resources, the preparedness plans that state or managers have on how to deal with it.”
During the first year, specialists are looking at existing rapid response plans, vulnerability assessments and communication plans. They take samples and track life cycles to try to understand how the mussels reproduce, how environmental conditions impact breeding and what kinds of treatments might work to stop the spread.
In the Southwest and along the Colorado River, the temperature of the water allows invasive species to breed multiple times a year, McMaster said. Each one can produce a million larvae. Not all survive: There are turbulent waters, areas with fewer nutrients, and other threats, like predators. But if they grow to adulthood they can layer on top of each other on underwater surfaces.
If left unchecked, invasive mussels could clog up pipelines that carry cooling water to turbines used to generate hydroelectric power. Without the cooling effect of the water, the turbine would “burn up” and power generation would shut down, McMaster said.
The goal at the end of the first year is mainly to inform the public. That means repeating the “clean, drain, dry” refrain as often as possible to anyone moving watercraft from one body of water to another, she said.
After that, a successful first-year response will also include setting up inspection and decontamination stations. Then, specialists move onto treatment options, McMaster said.
At Hoover Dam and Lake Mead, on the Nevada-Arizona border, managers took an aggressive treatment approach to avoid damage to the dam, she said. They used UV lights to stun and temporarily paralyze the microscopic veligers so they cannot attach inside the dam.
“Prevention is still the No. 1 goal,” McMaster said.
It’s the cheapest and least risky option, she said. Once an invasive mussel species arrives in an area, however, the costs can ramp up exponentially into the millions of taxpayer dollars. The goal is always to keep them at bay as much as possible, she said.
“They might be in the state of Colorado,” McMaster said, “but if you look at the overall percentage of uninfested areas, that’s still a lot of maintenance that’s not having to happen.”
Pest control on a private lake
On July 3, Colorado Parks and Wildlife staff discovered adult zebra mussels in a privately owned lake in western Eagle County, according to a news release.
CPW also identified additional zebra mussel veligers in the Colorado River near New Castle, Highline Lake and Mack Mesa Lake at Highline Lake State Park, the release said.
There were too many mussels in the Eagle County lake to count, Walters said in late August. Any hard structure in the lake and any underwater rocks were relatively covered in adult mussels, he said.
An invasive species specialist said in July that they believed the lake was an upstream source of the mussels in the Colorado River, and that an outlet from the lake was bringing zebra-mussel-infested water into the Colorado River, according to news reports.
Walters said that has not been confirmed.
“We are just continuing to try to monitor,” Walters said during an interview Aug. 29. “What I can say is that, to the best of our knowledge, there currently is no connection from this privately owned body of water into any of the river systems of the state.”
The state’s team spent about eight hours on Aug. 25 treating the lake with a copper-based molluscicide, a substance used to kill mollusks, he said.
Staff also sampled the private lake’s water Aug. 27 to make sure the treatment’s concentration was at the right level and planned to continue monitoring and treating the water throughout September, Walters said.
No boats or other watercraft were entering or exiting the lake, he said.
“It’ll be a long time before we know if it was truly effective at eradicating the zebra mussels,” he said.
The state focuses its monitoring efforts on public waters, mainly those with high recreational use. Motorboats and other types of boats are the main way the mussels spread, he said.
However, that doesn’t mean the teams don’t survey private ponds and lakes, Walters said.
After the state discovered zebra mussel veligers in the Colorado River and Grand Junction area, they started asking landowners if they could survey private lakes, ponds, gravel pits and more near the river. They often survey privately owned recreational areas, like water skiing clubs, he said.
“We have been trying to work with those private landowners to allow us access to come out and sample them for invasive species,” Walters said.
We need to keep our existing funding
But with thousands of private and public water bodies in the state, CPW alone is never going to be able to monitor all of them as frequently as the high-risk water bodies, he said.
The staff normally work in teams of two to inspect reservoirs and lakes. They pull fine mesh nets through the water to try to find microscopic veligers. They do shoreline surveys to look for razor sharp shells and other signs of invasive species.
On a small pond, the process can take one to two hours. On a big reservoir like Blue Mesa, Colorado’s largest reservoir, it would take six to eight hours, he said.
“I don’t think that there is ever going to be capacity to monitor every public and private body of water in the state of Colorado. And I don’t think that that’s ever going to be our expectation,” Walters said.
The aquatic nuisance species program has more resources than ever, but there’s always room for more, Walters said.
“At this time, we feel like we do have a good amount of resources to be able to sample the waters that we consider to be the highest priority,” he said.
Formerly, the team was based in Denver. Now, the state has established a traveling team to cover the Western Slope and another focused on the Grand Junction area.
They don’t need more authority to monitor private water bodies, he said.
“What we need is to continue to receive the funding that we are receiving today, and hope that does not get threatened if there’s any sort of budget cuts that are considered,” Walters said.
Aquatic nuisance species stamp sales cover about $2.4 million, or 50%, of the program’s annual funding needs. All motorboats and sailboats must have this stamp before launching in state waters, according to the CPW website.
Colorado state law calls on federal agencies, like the Bureau of Reclamation and U.S. Forest Service, to cover the other half of the funding needs since many high-risk waters in Colorado are federally owned or managed.
How are other water providers responding?
Zebra mussels go with the flow. They naturally move downstream with the river’s current, but boats traveling from one lake to another can carry them upstream.
That has upstream water managers, like Northern Water and Denver Water, keeping a close eye on developments along the Colorado River.
The Northern Colorado Water Conservancy District works with the federal government to transfer Colorado River water on the Western Slope through a series of reservoirs, pump stations and tunnels — called the Colorado-Big Thompson Project — to farmland and over 1 million residents from Fort Collins across northeastern Colorado.
Zebra mussels are such prolific reproducers they can clog up water delivery pipelines, the main concern for a water manager like Northern Water, spokesman Jeff Stahla said.
The C-BT project is no stranger to invasive species. In 2008, quagga mussels showed up in several reservoirs, including Grand Lake, Lake Granby and Shadow Mountain Reservoir. Another reservoir, Green Mountain, was also positive for quagga mussels in 2017.
All of the lakes are mussel-free and delisted, Stahla said. Now they’re tightening up security.
“The biggest task we can right now is to inspect those boats going into the reservoirs to make sure that they’re not going to be causing the problem,” he said.
Denver Water, which serves 1.5 million people in Denver and nearby suburbs, is also focused on inspecting and decontaminating boats.
“It’s a little unnerving. That’s for sure,” Brandon Ransom, recreation manager for Denver Water, said. “It’s certainly not welcome news that anybody in the state wants to see.”
The water provider also transfers Colorado River water through mountain tunnels and ditches to Front Range communities. Not only are the invasive mussels a concern for gates, valves, pipes and tunnels, they also cause problems for recreation. The shells are sharp enough to cut feet and the decaying mussels and old shells “smell to all heck,” Ransom said.
They haven’t launched new prevention efforts in response to zebra mussels reports, but that’s because the provider and its partner agencies already had fairly controlled boat launch and inspection procedures, he said.
They already intercepted adult zebra mussels on boats this year, he said. The latest catch was at Eleven Mile Reservoir in early October.
They’re trying to get the word out to people to make sure their boats and gear are clean, drained and dry. The zebra mussels like to hide in dark cavities, particularly around motors.
The good news is that Denver Water’s reservoirs, pipelines and tunnels on the Western Slope are upstream from the main infested areas, Ransom said.
“It doesn’t help me sleep at night, let’s put it that way,” he said. “We know that it’s closer and closer, and we’re trying to be extra vigilant when it comes to prevention in our waters.”
Print