The Río Grande o Futaleufú in Chubut, Argentina is a large tailwater river fed by the Futaleufú Dam and Amutui Quimey Reservoir, drawing its flow from a chain of lakes within the Los Alerces National Park system. Both names — Futaleufú (from the indigenous Mapuche language) and Río Grande (Spanish) — translate to "big river," a fitting description for this substantial waterway. From its source in the Argentine section, the river travels approximately 35 kilometres before crossing into Chile, where it enters Palena Province.

On the Argentine side, the river is characterized as a productive tailwater with cold, fertile water and a large, open character. It has been compared in scale and consistency to the Missouri River in Montana. The regulated flow from the dam makes it one of the more consistent fisheries in the region throughout the season. Float trips by drift boat are a common way to experience this stretch of river, and the surrounding landscape of the Southern Andes provides a dramatic backdrop.

It is worth noting that the high-gradient whitewater for which the Futaleufú is internationally known — including Class IV and Class V rapids — is located on the Chilean side of the border, not on the Argentine section described here. Paddlers seeking technical whitewater should be aware of this distinction. The Argentine reach is a large-volume river suited to float-style paddling rather than technical whitewater. Fly fishing, including catch-and-release, is a primary use of this stretch, and paddlers should expect to share the water with anglers, particularly during the fishing season.