Malleco River is a river in Malleco Province, La Araucanía Region, central Chile. It rises in the western slopes of the Andes, within the Tolhuaca National Park and near Tolhuaca Volcano.^[1] After passing by Tolhuaca, it drops into a 50 meter waterfall before continuing towards the Pacific.^[2] The river is a major tributary to the Vergara River, which is a tributary of the Biobío River. The Malleco Viaduct, built in 1890 and at the time the highest railroad bridge in the world, is the main landmark of the river and a candidate as a UNESCO World Heritage Site.^[3]