Area of Concern:
The area of concern includes all aquatic and riparian environments in the Flathead Basin
(Figure 2). The Flathead Basin encompasses 8,587 square miles (approximately six
million acres) in Northwest Montana and Southeast British Columbia, including Flathead
Lake, rivers, tributaries, lakes, ponds and wetlands. The basin drains the western and
southern slopes of Glacier National Park, as well as portions of the Bob Marshall
Wilderness Complex. The Flathead River is the largest tributary to the Clark Fork River,
which flows into Lake Pend Oreille, Idaho, and the Flathead Basin serves as the
headwaters for the Columbia River system.
The Flathead Basin is arguably the most intact native aquatic ecosystem in the United
States (outside of Alaska). For example, this Basin supports some of the last best habitat
for native cold‐water aquatic species in Montana, including bull and westslope cutthroat
trout. Within the Flathead Basin, AIS have the potential to significantly impact the fragile ecological balance between physical habitat and the native plants and animals
that depend on it (see Appendices C & D for a summary of AIS species currently posing
the greatest threats to the Flathead Basin). Impacts from AIS species already threaten
critical parts of this ecosystem. For example, the expansion of lake trout within the
Basin are negatively affecting bull trout. The impacts of nonnative fish occurrences may
vary throughout the state depending on the specific watershed and its current fish
populations. Since the Flathead Basin is located in the headwaters of the Columbia
River Basin and sustains numerous native fish populations, any infestation of AIS here
could result in serious adverse impacts to native fish and aquatic health within the Basin
as well as downstream.
Figure 2. Area of Concern: Flathead River Basin in northwestern Montana (USA) and southeastern British Columbia (Canada).
