Flowing through the heart of Chile's Biobío Region, the Río Biobío is one of the country's most significant river systems, stretching from the Andes to the Pacific Ocean. As the southernmost river of Chile's Mediterranean zone, it carries exceptional ecological importance, harboring the greatest fish species diversity of any river in the region — with 18 native fish species documented within its basin. The river has been substantially altered by the construction of major hydroelectric dams, most notably Pangue (operational since 1997) and Ralco (operational since 2005), which have reshaped flow regimes, habitat conditions, and fish populations throughout the system. Despite these pressures, the Río Biobío remains a destination of considerable interest for anglers drawn to both its native species and introduced salmonids.