The Río Desaguadero forms the natural boundary between Mendoza and San Luis provinces in western Argentina, running roughly north to south along the eastern edge of San Luis. The river is part of a much longer waterway system — known as the Bermejo or Vinchina in its upper reaches and the Salado further downstream — that ultimately joins the Río Colorado in La Pampa Province after a total course of approximately 1,498 km.

In the section relevant to San Luis, the river originates hydrologically from the overflow of the lagunas de Guanacache. In its initial stretch below the lagunas it flows intermittently, but after roughly 30 km it receives groundwater contributions from both the east and west, stabilizing into a medium-width channel with consistent flow. From that point onward, the river is considered navigable for canoes and small boats. National Route 7, which connects Mendoza and San Luis, crosses the river at the provincial border and represents a practical reference point for paddlers orienting themselves to the upper navigable section.

The river's intermittent character in its upper reaches is an important planning consideration: flow depends significantly on the water levels of the lagunas de Guanacache and the degree of upstream water extraction for irrigation, which has historically reduced the river's volume considerably. Multi-day kayak expeditions have been completed along this river system, traveling from the lagunas downstream through the Desaguadero and onward to the Atlantic — a journey of over 1,800 km — demonstrating that extended paddling is feasible when water levels permit.

The surrounding landscape is arid, consistent with the semi-arid character of this part of Argentina. The river runs through open, flat terrain with pronounced barrancas (steep riverbanks) that are visible evidence of the river's historically greater volume and flow.