Colorado Parks and Wildlife (CPW) confirmed earlier this month that invasive zebra mussels are present within the Colorado River. According to Colorado Public Radio, CPW officials found zebra mussels in Eagle County, near New Castle and the Highline Lake State Park. That means the Colorado River from its junction with the Roaring Fork to the Utah state line is positive for this invasive species.
Zebra mussels are tiny, but they’re a huge problem for waterbodies. Originally native to Europe, they spread rapidly and can cause severe ecological and structural problems. Zebra mussels are filter-feeders, and they subsist on tiny plankton. That plankton is often the basis of the food web in reservoirs and lakes. When that plankton is removed, it impacts everything from aquatic insect abundance to the health of trout and other fish.
Mussel infestations aren’t new to the United States. Most eastern rivers, and all the Great Lakes, are home to this invasive species. And as Elise Schmelzer wrote for The Denver Post, when zebra mussels were found in the Hudson River in New York, they “halved the amount of fish food available, shrank fish populations, reduced oxygen levels in the water, [and] changed the river’s chemistry.”
From a structural point of view, mussels have hard shells and attach themselves to any surface they can find. That means they’ll burrow into irrigation pipes, dam outlets, and other infrastructure used to deliver and control water flows. Removing mussels is costly and often ineffective. When it does succeed, it usually results in numerous other game fish dying.
In 2023, quagga mussels (similar to zebra mussels) were found in the Snake River near Twin Falls, Idaho. The Idaho Department of Fish & Game treated the river with a copper-based solution that killed significant amounts of fish, including native sturgeon.
That same approach apparently isn’t feasible on the Colorado River, according to Schmelzer in the Post. She spoke with Tina Bergonzini, the general manager of the Grand Valley Water Users Association, which has already treated some of its own irrigation equipment to prevent adult mussels from latching onto it. That cost $80,000, which was paid for by water users within the Association. To perform that same treatment in the Colorado River, Bergonzini said, would require “a line of rail cars” dumping the substance in the river.
CPW has not officially ruled out a treatment option. Currently, they’ve beefed up monitoring staff on the Roaring Fork and Colorado Rivers to get an idea of how many adult and juvenile mussels may be in the system.
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