The Collins River rises on the Cumberland Plateau in Grundy County, Tennessee near the town of Greutli-Laager . The Plateau is here capped largely by resistant Pennsylvanian Period sandstones. The Collins drains the Savage Gulf , a State Natural Area administered by the Department of Conservation and generally regarded as one of Tennessee's finest wilderness areas. Initially flowing roughly westward, the Collins then turns more northwest and then largely northward, flowing into Warren County. Flowing near Cardwell Mountain, it receives the surface drainage emenating from Cumberland Caverns , a cave developed in Mississippian Period limestone that is often considered to be one of the ten or so most extensive cavern systems in North America which is opened to the public during the travel season as a tourist attraction. Just below this point is the confluence with the Barren Fork River, a major tributary.

Several miles downstream, the waters become slacker as they begin to reach the embayment caused by Great Falls Dam . This dam is now operated by the Tennessee Valley Authority -- the only dam which it currently operates directly which is not on the Tennessee River or a Tennessee River tributary (although the dams on the Cumberland River system which are owned and operated by the United States Army Corps of Engineers are integrated into the TVA power system). This dam project well predates TVA; it was part of the assets of the former Tennessee Electric Power Company that TVA acquired in the late 1930s, a moved widely condemned at the time by many (generally outside the TVA service area) as "creeping socialism".

The Great Falls Dam creates a very deep reservoir; it floods the confluence of the Collins and the Rocky River with the Caney Fork River. This reservoir was a popular travel destination and site of cabins and cottages prior back in the period when there were few such developments in the southeastern United States; when other, much larger reservoirs were developed it fell largely into disuse as a recreational area, although a few of the old cabins remain and there are a few boat docks. Although very deep, the Great Falls Reservoir is quite small; all of the rivers flowed through relatively deep and narrow valleys at this point and the dam served largely to flood those valleys rather than much adjoining bottom land as has been the case with most of the reservoirs subsequently developed in the area.

At one time a considerable portion of the Collins was protected under the Tennessee Wild and Scenic Rivers Act, but area farmers succeded in having much of this protection removed, except from the part in Savage Gulf, because some provisions of the act regulate or prohibit certain agricultrual practices immediately adjacent to the river bank. In the upper reaches there are a considerable number of springs opening directly into the sides of the bluffs along the river and flowing directly into it. Apparently there are more springs doing so below where the water surface is typically located. The Collins is a very important scenic and natural resource.