Rio Maicuru is a remote and largely wild river flowing through the heart of Pará state in north-central Brazil, draining a vast watershed of approximately 21,917 square kilometers before emptying into the Amazon River system via the Lago Grande de Monte Alegre. Stretching between 547 and 610 kilometers in length, this substantial tributary originates in the Tumucumaque Mountains National Park on the Guyana Shield at an elevation of around 331 meters, descending through dense Amazonian rainforest to its mouth near Monte Alegre at just 3 meters above sea level. The river carries an average discharge of approximately 240 cubic meters per second near its mouth, reflecting the enormous volume of water that moves through this system year-round. The Maicuru and its tributaries — including the Igarapé Ipixuna, Igarapé Açu, Igarapé Fartura, Igarapé Jangada, Igarapé do Barreirinha, Igarapé 23, and Igarapé Santa Maria — form a complex network of waterways that support extraordinary aquatic biodiversity. Much of the watershed falls within or adjacent to protected areas, including the Maicuru Biological Reserve, making this one of the most pristine and scientifically significant river systems in the entire Amazon basin.