Invasive mussel remnants surface in Whitefish Lake
Laura Lundquist
(Missoula Current) A microscopic discovery in Whitefish Lake is a big reminder that the state of Montana needs to stay vigilant about stopping invasive aquatic species.
On Oct. 21, Montana Fish, Wildlife & Parks got a bit of a Halloween scare when a technician in the Aquatic Invasive Species Early Detection Laboratory found a microscopic larval mussel, or veliger, in a water sample collected from Whitefish Lake. Fortunately, the veliger, which resembles a tiny clam shell that measures about the width of two human hairs, was dead.
But FWP’s Aquatic Invasive Species team knew that the veliger’s presence could mean more mussels were in Whitefish Lake. So a dive team scoured the lake for invasive zebra or quagga mussels. They also collected additional water samples that they poured through with a very fine-toothed comb but fortunately, they found no evidence of live mussels.
However, FWP will continue sampling the water and use environmental DNA, or eDNA testing to be sure nothing was missed. Environmental DNA is DNA from skin, scales, eggs or waste that animals shed into the water as they swim or spawn, allowing scientists to detect species from a simple water sample. Scientists might not be able to see the species, but positive results from eDNA testing lets scientists know species are there.
“While the negative results are encouraging, they do not definitively rule out the presence of invasive mussels in the lake," said Tom Woolf, FWP’s aquatic invasive species supervisor. "We will continue to evaluate the initial finding and work with partners, including the City of Whitefish and Whitefish Lake Institute, to step up our sampling and monitoring of the lake in accordance with our mussel response plan.”
Biologists at the Flathead Lake Biological Station also volunteered their aid and expertise. While scientists don’t want mussels to invade Whitefish Lake, they definitely don’t want mussels showing up in Flathead Lake, which is part of the Columbia River watershed. The Columbia is the only river system in the nation that remains free of mussels, so Idaho, Washington and western Canada all have a vested interest in what Montana is doing to keep mussels away.
Invasive mussels, including zebra and quagga mussels, pose a significant threat to Montana’s waterways. Even though they are tiny - about the size of a pistachio nut - they can reproduce rapidly, forming colonies that cover every underwater surface. So they can clog water infrastructure and disrupt aquatic ecosystems. This spring, FWP added a new species, the golden mussel, to its list of invasive aquatic species after it first showed up in California in fall 2024.
Montana had its first scare in 2016, when mussel larvae were detected in two water samples from Tiber Reservoir about 15 miles southeast of Shelby. Then a third positive sample showed up in Canyon Ferry.
After that, the Montana Legislature allocated funding for FWP to bolster its boat inspection program to detect mussels before they reached Montana’s lakes and rivers. In 2025, the Legislature passed a law nearly doubling the fines for failing to stop at watercraft check stations to $700 and $1400 for first and subsequent offenses.
Biologists also did intensive sampling for two years in Tiber and Canyon Ferry reservoirs. They found mussel eDNA in Tiber Reservoir in 2017 but nothing after that. Woolf said in 2019 that mussels might have been in Tiber but couldn’t get established because the reservoir is partially drained each year, dropping the water level about 15 feet, exposing the shallows.
Keeping mussels out of Montana remains an FWP priority. Unfortunately, invasive mussels are moving closer to Montana’s borders, having shown up in the Snake River in Idaho and the lower Missouri River in North Dakota.
This year, FWP had 36 check stations working across the state to stop any boats that might be carrying invasive mussels. They inspected more than 91,000 watercraft and managed to catch 28 mussel-fouled boats this summer. The mussel-fouled boats often come from Lake Powell or Lake Mead in the Southwest or the Great Lakes. Thus, mussels were found on a number of boats from Minnesota, Arizona and Nevada.
“We can’t let up. We have to protect our waters,” said Woolf. “All watercraft should be cleaned, drained, and dried before being moved between waterbodies, and boaters should stop at required watercraft inspection stations.”
Contact reporter Laura Lundquist at lundquist@missoulacurrent.com.