Barcelos (also Barcellos), formerly Mariuá, is a municipality located in the state of Amazonas, northern Brazil. Its population was 27,638 (2020) and its area is 122,476 square kilometres (47,288 sq mi). It is the second largest municipality in Brazil (behind Altamira, Pará); equivalent in size to New York state in the United States and slightly larger than North Korea. Since 1994, Barcelos has been the host of an annual festival celebrating ornamental fish, which is a significant source of income for the region. Project Piaba uses Barcelos as the starting point for their annual research expedition into the Rio Negro area. The region is the biggest exporter of this particular fish in Brazil with over 19 million specimen exported into Europe, Asia and USA. Barcelos is known for Ecotourism.