The river contains 3.5 miles of continuous Class III-V rapids , and a number of impressive individual rapids. Rapid River flows in a northwesterly direction and drops approximately 156 feet in six miles. The river flow is measured and regulated at Middle Dam to provide the necessary flow rate in the Androscoggin River for hydropower operations. The average flow is upward to 1,000 cubic feet per second, producing four to six-foot standing waves.
Rapid River is known locally and regionally as a premier fishing resource.
The entire Rapid River is a nursery for significant populations of brook trout and landlocked salmon. Pond in the River and several small pools in the river are spawning areas for trout and salmon. Rapid River is undeveloped, except for one cabin, and is exceptionally scenic. A cluster of old-growth white pine trees grow near Smooth Ledge. Dense stands of white pine, balsam fir, northern white cedar, and red spruce grow along the river banks.