The upper reaches of the Amazon River are the Ucayali River and the Maranhón River, which originate from the eastern slope of the Western Cordillera of the Andes in southern and western Peru respectively. After crossing the mountains, the two rivers merge near Nauta and are called the Amazon River. From then on, it flows eastward through the Amazon Plain, and the middle reaches to Manaus are the river section; the lower reaches below Manaus to the river mouth are the river section, and finally it flows into the Atlantic Ocean near Marajo Island. The source is the Ucayali River, which originates in southern Peru. The entire Amazon River is more than 6,400 kilometers long