Rio Jari is a magnificent and largely wild river stretching approximately 790 kilometers (490 miles) through the remote rainforests of northeastern Brazil, forming the natural border between the states of Pará and Amapá. Fed by headwaters originating in the Tumuk Humak Mountains to the south, the river flows through the Uatuma-Trombetas moist forests ecoregion before emptying into the Amazon River near the municipalities of Almeirim in Pará and Vitória do Jari in Amapá. With a drainage basin covering roughly 60,000 square kilometers and average discharge ranging from 1,005 to 1,880 cubic meters per second, the Jari is a powerful and dynamic waterway that borders the Guiana Highlands and the Guianas to the northwest. Part of its basin falls within the Maicuru Biological Reserve, and the broader Calha Norte region — one of the most biologically intact and least-studied stretches of Amazonian rainforest — surrounds much of the watershed. The river's mouth sits opposite Ilha Grande de Gurupá, the second-largest island of the Amazon River Delta, giving the lower river a broad, estuarine character that transitions dramatically as you move upstream into tighter, more forested reaches. For anglers willing to make the journey into this remote corner of the Amazon Basin, Rio Jari represents one of the last truly frontier fishing experiences in South America.