Río Los Sosa is a mountain river flowing through the Yungas ecoregion of central-western Tucumán Province, Argentina, within the Reserva Provincial Los Sosa. The river runs along Ruta Provincial 307, the main corridor connecting the lowlands to the Valle de Tafí and the Valles Calchaquíes, and drains into the Salí-Dulce basin, ultimately reaching Laguna Mar Chiquita in Córdoba. The river descends through a pronounced altitudinal gradient, from roughly 500 to 1,900 meters above sea level, passing through successive vegetation zones of the Yungas as it drops.

For whitewater paddlers, the river offers multiple sections of varying difficulty. The Heladera section (Class III–IV) puts in at an old house on river left just after the small creek La Heladera, with the takeout where Route 307 approaches the river near an empty house with a single track to the water. The Fin del Mundo section (Class III–IV) begins at the Heladera takeout and ends at the Route 307 pullout past the Indian statue parking area on the last U-turn. The Indio Vialidad section (Class IV–V) starts at the Fin del Mundo takeout and finishes at the Vialidad house. The Vialidad Aforo section (Class II–III) runs from the Vialidad house to the Aforo station. Below that, a roughly 4-kilometer stretch beginning at the Aforo station offers continuous rapids at Class II–III, with multiple takeout options along the left bank where the road parallels the river closely.

The climate in the valley is warm and humid, moderated by elevation, with the bulk of precipitation falling in summer (the austral summer, roughly November through March), when annual totals can reach 2,700 mm. Winter months bring persistent fog that maintains humidity even outside the rainy season. Higher water levels during the summer rainy season will generally increase the intensity of the rapids.

The river corridor supports notably rich birdlife, with 118 species recorded along its length, including the torrent duck (Merganetta armata) and the Rufous-throated dipper (Cinclus schulzi), both indicators of good river habitat quality. The reserve encompasses approximately 890 hectares of protected Yungas habitat, and the road access along Route 307 makes logistics relatively straightforward for most sections.