It is one of the most threatened waterfowl species in the world, with possibly fewer than 250 birds in the wild and a small number kept in captivity in Brazil.

This merganser is a dark, slender duck with a shiny dark-green hood with a long crest, which is usually shorter and more worn-looking in females.

Depending on the availability of suitable nesting and feeding sites, Brazilian merganser pairs occupy permanent territories of 8-to-14-kilometre (5.0 to 8.7 mi) stretches of rivers.

[1] Tree cavities, rock crevices, or disused burrows predominantly made by armadillos are the ideal places for these mergansers to build their nests.

It is thought the breeding season is during the austral winter, when rain is minimal and water levels are low, but it may vary geographically.

Brazilian mergansers are very territorial birds defending large stretches of river and the land surrounding the fast-flowing water.

A major threat to the birds' survival is the issue of silting of rivers caused by the expansion of farming activities, mining, watershed degradation and soil erosion, as well as deforestation.

Current traditional soil management and use practices in the region from farming may bring about serious damage regarding conservation of natural resources, especially water, on which the Brazilian mergansers and the farmers themselves are dependent.

It is common in the region to see farmers burning forest areas causing environmental damage to the natural vegetation and soils and the resident species.

The dams flood suitable habitat, especially in Brazil and Paraguay, where the Brazilian mergansers build their nests and lay their eggs.

Activities such as canoeing and rafting disturb the natural habitats for the Brazilian mergansers that thrive on the rapid-rivers, interrupting breeding patterns.

[citation needed] People hunting the birds for food and collecting them for exhibition specimens contributed to the decline of the species.