Flowing out of the coastal mountain range southwest of Paillaco, the Río Collileufu is a third-order stream that winds northward through the Región de Los Ríos before emptying into the Río San Pedro near the town of Los Lagos. Part of the broader Cuenca del Río Valdivia watershed, this river moves through a richly biodiverse riparian corridor and offers a genuine backcountry trout fishing experience in one of southern Chile's most ecologically vibrant landscapes. The river's flow varies considerably throughout the year, which shapes both its character and its fishability across the seasons.