The Maicuru River is a river of Pará state in north-central Brazil, a tributary of the Amazon that discharges into that river via the Lago Grande de Monte Alegre. The river basin lies partly within the 4245819 ha Grão-Pará Ecological Station, the largest fully protected tropical forest conservation unit on the planet. Part of the river's basin is in the Maicuru Biological Reserve. The river is also fed by streams in the 216601 ha Mulata National Forest, a sustainable use conservation unit created in 2001.