Flowing eastward from the high Sierras Grandes of Córdoba Province, the Río Segundo — also known by its indigenous Comechingón name, Xanaes — stretches approximately 340 kilometers from its origins in the Paravachasca Valley to its terminus in the saline Laguna Mar Chiquita. The river is born at the confluence of the Los Molinos and Anizacate rivers, at elevations near 2,000 meters above sea level on the eastern slopes of the Cumbres de Achala. From there it descends through mountain terrain before transitioning into the broad, flat Pampas plains, where it meanders in a predominantly east-northeast direction and eventually divides into two main arms that empty into Mar Chiquita. A significant feature along its course is the Los Molinos Reservoir, created by the Los Molinos Dam — constructed between 1948 and 1953 — which regulates flow and generates approximately 56.5 megawatts of hydroelectric power. The river is part of an endorheic basin, meaning it drains entirely into the interior without connection to the ocean or the Paraná River system, a characteristic that has shaped its unique fish community.