The Río Negro is one of the principal tributaries of the Rahue River in southern Chile, draining part of the eastern slopes of the Cordillera Pelada. It originates in the Coastal Precordillera and flows from south to north, joining the Rahue at an elevation of approximately 26 meters. The commune of Río Negro takes its name from the river.

Near Hornopirén, the Río Negro is known for its steep basalt drops, giving it a distinctly technical character. This contrasts sharply with the nearby Río Blanco, which features smooth granite boulders and glacier-fed blue water. The two rivers run only a few miles apart but present entirely different paddling experiences. The Río Negro's basalt geology and steep gradient suggest demanding whitewater that will appeal to paddlers comfortable with committing drops rather than continuous boulder-garden style rapids.

The rivers of this part of southern Chile are generally noted for their pristine water quality. Hornopirén itself sits at the northern edge of Patagonia and is accessible from Puerto Montt via a combination of road and small ferry, making logistics for a visit more involved than for rivers closer to the main highway corridor. Paddlers planning a trip should factor in the remoteness of the area and the access requirements when organizing shuttle and gear transport.