The Río Chimehuín originates at Lago Huechulafquen in the northwest of Neuquén Province, Patagonia, and flows approximately 53 kilometers before merging with the Aluminé River to form the Collón Curá River. The river passes by the city of Junín de los Andes along its course. The upper section, from the lake to a few kilometers before Junín de los Andes, falls within the Área Natural Protegida Boca del Chimehuin.

For rafting, the standard run covers nearly 10 kilometers and passes through eight rapids ranging from Grade 2+ to Grade 3, making it suitable for families and paddlers without prior whitewater experience. Named features along this stretch include the herradura (horseshoe), the rápido del sauce (willow's rapid), the boca del lobo (wolf's mouth), the pozón de las viudas (widows' pool), and the pared del viento (wind's wall). The float takes approximately one and a half hours on the water. The typical put-in is accessed from San Martín de los Andes via Ruta Nacional 40 toward Junín de los Andes, reaching the head of the river at Lago Huechulafquen.

Water levels and character vary significantly by season. In October, snowmelt produces waves exceeding two meters in height, creating more demanding conditions. By January and February, flows drop and the water warms, allowing paddlers to see the riverbed clearly and encounter features such as steps, holes, slides, and rock formations. The river's flow is directly dependent on snowmelt from the surrounding mountains.

The climate is high mountain in character, with cold temperatures and significant rainfall. Summer temperatures can reach 33°C, while winter temperatures can fall to -15°C. The rafting season runs through spring and summer.

Views of Volcán Lanín are visible from the river corridor. The Río Chimehuín is widely regarded as one of Patagonia's premier fly-fishing rivers, known for wild rainbow and brown trout, and the river sees considerable angling traffic alongside rafting activity. Guided rafting operators based in San Martín de los Andes provide all required equipment, including neoprene wetsuits, life preservers, waterproof jackets, neoprene boots, and helmets.