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Status of Dreissenids Near the CRB

Since their introduction to the Great Lakes region of North America in the 1980s, invasive dreissenid mussels [zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena rostriformis bugensis)], have expanded their distribution across North America (Figures 1 and 2). Each year, the states of Washington, Oregon, Idaho, and Montana intercept dreissenid-fouled watercraft that originated from locations throughout North America.


In 2016, invasive mussel larvae were discovered in Tiber and Canyon Ferry Reservoirs in Montana—this was the first documented detection of dreissenids near the perimeter of the Columbia River Basin (CRB). The expansion of dreissenids, primarily via watercraft vectors, precipitates the need for contingency plans and other planning efforts to prepare entities for an introduction of dreissenids (Bossenbroek et al. 2007). The detection of dreissenids in Montana are not displayed on the maps below because subsequent annual sampling has neither confirmed, nor supported, a positive identification of dreissenids after the initial veliger detections in 2016.

Species observations:

1 specimen

2 to 5 specimens

6 to 10 specimens

11 to 19 specimens

20 or more specimens

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