Maullín River (Spanish: Río Maullín) is a river of Chile located in the Los Lagos Region. The river originates as the outflow of Llanquihue Lake, and flows generally southwestward, over a number of small waterfalls, emptying into the Gulf of Coronados.^[3] The lower course of the river is a tidal estuary. The wetlands of Maullín stand out for their diversity of aquatic birds when compared to other locations of the Chilean coast.^[4] In the estuary Laguna Quenuir is the place known to have the largest diversity of bird fauna.^[4]

Franciscan Friar Francisco Alvarez Villanueva mention in 1780 Maullín River as the limit between the Spanish possessions and the "Cunco nation" to the north.^[5]

The river was first explored extensively in 1856 and 1857 by the Chilean Navy officers Francisco Hudson and Francisco Vidal Gormaz.^[6] The area around Llanquihue Lake was settled in the second half of the 19th century by German immigrants, who received land from the government in a scheme to encourage settlement in this area.^[7]