Embalse Río Hondo sits on the provincial boundary between Tucumán and Santiago del Estero, approximately 3.5 km upstream from the city of Termas de Río Hondo. The reservoir covers roughly 330 km² (44,000 hectares), stretching about 19 km in length and 17 km in width, at an elevation of 272 meters above sea level. The lake is divided roughly equally between the two provinces, though virtually all of its freshwater inflow originates from Tucumán via the rivers Salí, Gastona, Medina, Mayo, Marapa, Lules, and Chico, all draining the Aconquija mountain system.

The dam structure — known as the Dique Frontal Río Hondo — is a mixed earth and reinforced concrete system. The concrete section, 206 meters long with a maximum height of 30 meters, houses the hydroelectric plant (operational since 1976) along with control gates and turbine intakes. The total dam length reaches 4,325 meters. Paddlers should be aware of the dam infrastructure and associated water management operations, which can affect flow and water levels across this large impoundment.

The reservoir supports a notable fishery, with species including bogas, sábalos, bagres, tarariras, pacúes, surubíes, and dorados reaching up to 25 kg. A national dorado fishing championship takes place annually in October, which will bring increased boat traffic to the water during that period. The scale of the reservoir — nearly 20 km across in both dimensions — means open-water crossings can expose paddlers to significant wind and wave exposure, and the flat, expansive character of the lake offers little natural shelter in deteriorating conditions.