The Río Bermejo is a free-flowing river in northern Argentina that traverses the Gran Chaco region, notable for being undammed along its entire length. In the plains of Chaco, the river splits into two branches near the Tropic of Capricorn: the northern branch, known as the Río Teuco or Bermejo Nuevo, which serves as the main stem, and the southern branch, the intermittent and meandering Río Bermejito, which follows the river's former channel. The two branches rejoin near Villa Río Bermejito. The river carries heavy loads of red-colored sediment, which gives it its name, and these sediments produce irregular accumulations that can alter the river's course over time, leaving older channels as wet depressions.

The Bermejo is generally considered non-navigable for commercial purposes due to shallow waters and the enormous sediment load it carries. Paddling excursions do take place, however, particularly in the stretch running through and toward Parque Nacional El Impenetrable. Puerto San Jorge at Camping La Fidelidad serves as an access point where guided boat trips on the river are offered. These outings are personalized and require advance reservation. Glamping El Bermejito, located along the Río Bermejito, offers kayak excursions on that secondary branch.

Summer rainfall in the mountains of Jujuy, Salta, and southern Bolivia feeds the river and generates significant flooding that spreads across the Chaco plains, creating lagoons and wetlands. These seasonal floods are a defining characteristic of the river's hydrology and shape the surrounding ecosystem considerably. During the dry season, water levels drop and the river's course becomes more constrained.

Wildlife along the river is abundant. Timbós, algarrobos, palos santos, and alisales line the banks, and fauna regularly observed includes giant anteaters, peccaries, tapirs, yacarés, capybaras, herons, ducks, and skimmers. Tracks of jaguar and puma have been reported on sandbars. The river functions as a natural wildlife corridor connecting the Yungas cloud forests with the Gran Chaco, making it ecologically significant for species movement and conservation. The Río Bermejito also passes near the ruins of former colonial settlements, including Concepción del Bermejo, San Bernardo de Vértiz, and La Cangayé.