Carlos Anwandter Nature Sanctuary (Spanish: Santuario de la naturaleza Carlos Anwandter) is protected wetland in Cruces River about 15 km (9 mi) north of Valdivia, Chile. The sanctuary is named after the German politician Carlos Anwandter who settled in Valdivia during the 1850s. The wetlands in the sanctuary are inhabited by many bird species including Black-necked Swans.
In 2004, the Valdivia Pulp Mill was opened in San José de la Mariquina located 25 km (16 mi) northeast near Cruces River. The emblematic Black-necked Swans started at that time to die and migrate. Ecologists and people from the university UACh in Valdivia accused the forestry enterprise CELCO to being polluting the river. The pulp mill was forced to close while the case was investigated . Even in 2006, the Latin American water tribunal recommended to close down the mill .
As of November 2008, the case against CELCO was still being debate in court. In the mean time, other hypotheses have been proposed to explain the dramatic decrease of the swan's population.