The Río Quinto, also known as the Popopis, is a distinctive and ecologically significant waterway that winds through the heart of central Argentina, traversing the province of San Luis before continuing into the southern reaches of Córdoba. What makes this river particularly unusual among Argentine waterways is its endorheic character — it does not drain to the sea, but instead flows inward, connecting sierra landscapes, open plains, and a rich network of regional ecosystems. The river originates in the Sierra de San Luis, with its headwaters traceable either to the springs of Cerro Retama or to the slopes of Cerro Tomolasta, giving it a mountain-born character that gradually transitions into the broader lowland terrain of the Córdoba interior. This journey from sierra to plain creates a diverse range of habitats along its course, making it a water body of genuine interest to anglers exploring the less-traveled fishing destinations of central Argentina.