The Cold River begins in the hills of northwest Acworth and Unity at Crescent Lake (1215 feet above sea level). Over its 22 mile course from the Crescent Lake dam to the Connecticut River in Walpole the river drops 979 feet.
The Cold River tumbles first as a stream over the small dam at the east end of Crescent Lake. This first 1.3 miles is the river’s steepest stretch, with a gradient dropping 66 ft/mile. The river slows next to meander through the marsh that was once a mill pond behind the old Keyes Hollow dam.

Below the Deep Hole to the river's end, the valley broadens and the Cold River’s swift current carries it over a cobbled river bottom with an average gradient of 40 ft/mile. It crosses under McDermott Covered Bridge in Langdon before entering Vilas Pool, created by a dam at the head of a small gorge. Vilas Pool is a popular place for picnicking, boating, swimming and many summer events in the town of Alstead.

The river flows through Alstead and its valley broadens again. After several miles, the valley walls close sharply and the river drops over the spectacular Drewsville Gorge, where 25 foot cliffs rise above several small waterfalls. Below this gorge, the Cold River cuts through deep sand and gravel deposits that once formed a great delta in the ancient glacial Lake Hitchcock.
As the Cold River joins the Connecticut , it deposits its own sand and gravel in a sand bar that sweeps into the larger and slower Connecticut.