The Belly River originates in northwestern Montana at
Helen Lake, near the base of
Ahern Peak in
Glacier National Park. It flows north across the
49th parallel north into
Alberta near
Chief Mountain, in the east of the
Waterton Lakes National Park. It continues north, crossed by
Highway 6 and
Highway 5, passes near the communities of
Hill Spring and
Glenwood, then turns northeast. It is crossed by
Highway 2 north of
Stand Off, then continues north along the base of the Mokowan Ridge, where it receives the waters of the
Waterton River. Its flow becomes
meandered before the river turns east around the Wild Turnip Hill, then it empties into the
Oldman River west of
Coalhurst, south of
Highway 3, at an elevation of . ==Tributaries==