In 2004 and 2005 thousands of black-necked swans in the Carlos Anwandter Nature Sanctuary in Chile died or migrated away following major contamination by Valdivia Pulp Mill located on the Cruces River which feeds the wetlands. By August 2005 the birds in the Sanctuary had been "wiped out"; only four birds could be observed from a population formerly estimated at 5000 birds. Autopsies on dead swans attributed the deaths to high levels of iron and other metals polluting the water.[
