The Teton River watershed drains , in Idaho and in Wyoming. The river mainstem is formed near
Victor in
Teton County, Idaho, near the Wyoming state line, by the confluence of Warm Creek (Trail Creek watershed) and Drake Creek. It is joined by several additional creeks that descend from surrounding
Teton, Big Hole, and
Snake River mountain ranges. The majority of flows to the Teton River come from tributaries draining the western flank of the Tetons, including Trail, Fox, Teton, and South Leigh creeks. Trail Creek descends along Highway 22 from the
Caribou-Targhee National Forest in Idaho, meeting the other creeks from the south. The river flows north in a slow meandering course through a broad flat valley called the
Teton Basin (formerly known as "
Pierre's Hole"), flanked by the Teton Range to the east and the
Big Hole Mountains to the west. Much of the river's upper course in the Teton Basin is surrounded by extensive
wetlands. After emerging from the north end of the Teton Basin, the Teton River enters the nearly inaccessible
Teton Canyon, approximately long, along the Teton-
Fremont county line. There it is joined by Badger Creek and
Bitch Creek from the east, then turns almost 90 degrees west, and is joined by
Canyon Creek from the south. After passing through the failed
Teton Dam site, north and east of
Newdale, the Teton River bifurcates into two
distributaries some four miles downstream, just north of
Teton, one called the South Fork Teton River (also called the South Teton River) and the other called North Fork Teton River (also known as the Teton River). The South Teton River travels generally southwest until it joins Henry's Fork west of
Rexburg at the southwest end of a large inland
delta region on the Henry's Fork, essentially merging with the delta from the east as one of its channels. The Teton River itself (North Fork Teton) continues to travel west, where it joins the Henrys Fork at Warm Slough near Rexburg, approximately seven miles upstream of the confluence with the Snake River. ==Ecology==