The Río Tercero (Ctalamochita) originates in the Sierras de Córdoba near Cerro Champaquí and flows through the Valle de Calamuchita before crossing the plains, covering 307 kilometres before joining the Carcarañá River. Its drainage basin spans approximately 21,000 square kilometres, and mean flow is around 21–27 cubic metres per second. The river's name "Tercero" dates to the 18th century, when it was counted as the third river south of Córdoba city; "Ctalamochita" is believed to derive from a Native American word meaning "area of many trees." In 1984, the provincial legislature formally adopted the combined name Río Tercero (Ctalamochita).

Four dams along the river — Cerro Pelado, Arroyo Corto, Embalse Río Tercero (also called Dique Ministro Pistarini, completed in 1936 and covering 54.3 square kilometres), and Piedras Moras (inaugurated 1979, covering 600–900 hectares with a maximum depth of 34 metres) — regulate flow and generate hydroelectricity. These reservoirs are also used for water sports and tourism. The Piedras Moras Reservoir sits 2 km from the town of Almafuerte and 101 km from Córdoba city via Provincial Route 6.

For paddlers, kayak routes include a traverse of the Contraembalse Arroyo Corto in the Valle de Calamuchita, a roughly 16-kilometre out-and-back trip with an estimated six hours of paddling and trekking. A multi-day river journey from Almafuerte to Villa María covering approximately 110 kilometres has been undertaken, with paddlers camping on the riverbanks over three days. Water levels should be checked before attempting the Río Tercero–Villa María stretch. The river corridor passes near the towns of Amboy, Villa Amancay, and Embalse, offering mountain scenery and riparian vegetation.

The river supports notable biodiversity, including native fish species such as dorado and tararira. Sport fishing — both wading and float fishing — is actively practiced along accessible stretches, with mandatory catch-and-release rules in place for dorado. The surrounding riparian habitat sustains birds, mammals, and amphibians, though the river faces pressures from contamination and habitat degradation. The best season for water-based activities on the reservoirs is summer and early autumn; at Piedras Moras, winter water temperatures drop to around 10 °C.