Possible mussel detection in Missouri River

Preliminary test results have indicated another possible detection of mussel larvae south of Canyon Ferry Reservoir in the Missouri River, although additional lab work is needed to confirm the detection.

Montana Fish, Wildlife and Parks spokesman Greg Lemon said Monday evening that a water sample taken from the York Islands fishing access south of Townshend was found to be “suspect” during initial testing by state scientists. He said additional testing is needed to confirm whether the sample contained larvae from zebra or quagga mussels, two species of invasive mussel known to multiply aggressively and generate costly damage to aquatic ecosystems and infrastructure.

The finding comes about two weeks after mussel larvae, known as “veligers,” were confirmed for the first time in Montana waters at Tiber Reservoir. Another sample taken from upstream in Canyon Ferry was inconclusive, but a visual microscopy test indicated the veligers were present in that water body as well.

Lemon said an additional sample from the Milk River, downstream of Nelson, also returned an inconclusive result. However, he said state scientists believe the veliger was already dead before it ended up in the water.

“Basically what we found in the water sample was essentially the husk of the larva,” he said. “It didn’t have any intact organs ... which indicates the larva dried out at some point prior to the introduction.”

State fisheries officials have for years worked to keep invasive mussels out of Montana waterways, and are working to establish a plan to contain any contaminated waterways. About 540 water samples were collected from 141 bodies of water this summer, Lemon said, and the wildlife agency is still working through the rest of those taken from the Missouri River drainage.

Samples from west of the divide have yet to be tested, but to date no mussels or mussel larvae have been detected in the Columbia River Basin.

While news of mussel larvae in Montana has rippled through the state and mussel-free states downstream, no reproducing adults have been found.

Diving teams wrapped up surveys of Canyon Ferry on Monday without finding any of the tiny mollusks attached to docks along the shore, keeping alive the possibility that the larvae were only recently introduced.

Reporter Sam Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com.