The source of the Amazon is in the Andes Mountains of western South America. It flows east from there to the Atlantic Ocean. Most of the huge river and its many tributaries are in the country of Brazil. There are many places on the Amazon where a person on one side of the river cannot see the other side. The Brazilians call the Amazon the "River Sea." The Amazon is navigable from the ocean to Peru. Ocean ships can travel on the Amazon all the way across Brazil, and most of South America, to the city of Iquitos in Peru.