What is the largest river by volume in Montana that also double Downtown Missoula's rough boundaries to its south?
Downtown Missoula:  Downtown Missoula's rough boundaries are the Clark Fork River to its south, Madison St. to its east, the old U.S 93 highway/ North Orange St. to its west, and West Alder St. to its north, though parts south of the Clark Fork River are also at times mentioned. Clark Fork River:  The largest river by volume in Montana, it drains an extensive region of the Rocky Mountains in western Montana and northern Idaho in the watershed of the Columbia River.
Clark Fork River