The Natchaug River is a 17.9-mile-long (28.8 km) river in Windham and Tolland Counties in Connecticut. The Natchaug River is formed in Eastford, Connecticut at the confluence of Bigelow Brook and the Still River. It then flows to the south, paralleling Connecticut Route 198. The river also runs along (and in a few cases through) the western border of the main Natchaug State Forest parcel. Where the river briefly passes through Natchaug State Forest, locals can have picnics along the river, and enjoy white-water rafting through the abundant rapids and swimming in the river's clean water.