It’s a bluebird day at West and East Lake in Grand Junction, and Maddie Baker is throwing a plankton tow net into the water, and dragging it back to her.
“This is made of a 64 micrometer mesh, so that allows us to trap the veligers in their juvenile form, where they are microscopic and invisible to the eye,” she explains.
Baker is an invasive species specialist for Colorado Parks and Wildlife. A veliger is the larval form of many kinds of mollusks, including the invasive—and pervasive—zebra mussel.
Baker doesn’t have to tow the plankton net to know the mussels are here. She picks mussel after mussel off of a concrete platform that gives anglers access to the lake.
“It sucks, yeah,” she says. “It's a very unfortunate realization for us to come to. And it shows us that this population is already well established in this body of water, if we can find adults with relative ease.”
Part of the reason a zebra mussel infestation is such bad news is how durable they are. Baker says they attach to hard surfaces using bissell threads.
“It's organic material that they secrete from their body that forms both a physical and chemical bond with whatever hard surface they're attaching to,” Baker explains. “So this does last for their life and beyond.”
Quagga mussels, zebra mussels’ close relatives, and other aquatic nuisance species, have made their presence felt as reservoirs in the Colorado River Basin, like Lake Powell and Lake Mead.
“At places like Lake Powell, where the water level fluctuates pretty often, you will see mussels that are still attached to canyon walls even after they're already dead,” Baker says of the strength of bissell threads. “Just because those bonds are really lasting”.
Another alarming zebra mussel trait is how fast they reproduce.
“Each one of these can produce a million offspring and then each of those million offspring produces a million every single year,” Baker says, showing off a handful of zebra mussels, freshly plucked from the concrete platform.
“So the notion of these attaching inside of our pipes or hydroelectric infrastructure–dams–is very concerning,” she says.
Zebra mussels originally came to North America through shipping vessels traveling in the St. Lawrence Seaway from Eastern Europe. In the Great Lakes region, they’ve wreaked havoc on water infrastructure, and caused millions of dollars in damage.
Morgan Hoffmann is CPW’s Early Detection and Rapid Response specialist. She’s holding up what’s essentially a little piece of pipe that stays in for mussels to attach to in their juvenile stage, when they're still too small to see with the naked eye.
“On these, we're really targeting the settler stage of the zebra mussels,” Hoffman says. “So when we pull these out of the water, we feel the pipe and we're looking for a sandpaper-like texture on that stage of the mussel.”
There are five bodies of water in Colorado that are officially considered “infested,” which means that the zebra mussels have established a reproducing population, with multiple life stages detected. In addition to West and East Lake, the list includes Highline Lake, Mack Mesa Lake, the Colorado River from the 32 Road bridge to the Colorado-Utah state line, and a private body of water in Eagle County.
The Colorado River is considered mussel-free from its headwaters to the confluence with the Roaring Fork River in Garfield County. Downstream of that point, CPW hasn’t found any adults, but they have found the veligers.
West and East Lake drains into the Colorado River, via a nearby channel. The Colorado River is already under a lot of pressure. Climate change is contributing to a historic drought, and there’s a lot of demand for water from both agriculture and growing communities on both the Western Slope and the Front Range.
CPW’s Public Information Officer for its Northwest Region, Rachael Gonzales, said zebra mussels add another layer of stress to aquatic ecosystems.
“They also have an impact to the environment, and specifically to the water because they're filter feeders,” she said. “So they are filtering every good nutrient that our native fish need to survive.”
It’s because of these threats that CPW is taking zebra mussels so seriously, and has increased its sampling efforts all the way to the river’s headwaters. Hoffmann oversees the program, along with the agency’s testing lab in Denver.
“I'm feeling confident in our program overall,” she said. “Since we found them, it's kind of proven that our sampling and monitoring program is effective and the way we've designed it is working. So we're detecting these pretty quickly, which is what we want to do.”
Robert Walter, CPW’s invasive species program manager, said that because of the severity of the threat, they’ve been able to access additional resources, including from the federal government.
“Because we are collaborating with them so regularly, we're not only able to do what we know or are more traditional sampling technologies, but we are also able to utilize those that are out there on the cutting edge to give us the highest probability of finding these things out in the environment,” he said.
He said they worked directly with the Bureau of Reclamation to develop testing methods to detect zebra mussel DNA, and they worked with the U.S. Geological Survey to deploy an autonomous sampler on the Colorado River—a new piece of technology.
But Gonzales wants to emphasize that it’s not just professionals out in the field that can make a difference. Zebra mussels spread from one body of water to another primarily through people.
“We see a lot of fall fishing, we also see waterfowl hunting,” Gonzales said. “Taking a couple extra minutes when you're done and cleaning your waders is going to go a long way to protect our bodies of water.”
The more the public can help with the risks, Gonzales says the better they can protect Colorado’s infrastructure, its native species, and a way of life that depends on healthy waters.
CPW lists gear-cleaning station locations across the state on its website, and the agency is asking the public to report any potential sightings of zebra mussels in local bodies of water.
Copyright 2025 Rocky Mountain Community Radio. This story was shared via Rocky Mountain Community Radio, a network of public media stations in Colorado, Wyoming, Utah, and New Mexico, including Aspen Public Radio.
