Peru is located on the central western coast of South America facing the Pacific Ocean. It borders Ecuador and Colombia to the north, Brazil to the east, Bolivia to the southeast, Chile to the south, and the Pacific Ocean to the west. The Andes mountains run parallel to the Pacific Ocean. Peru has three main geographic regions. The costa (coast), to the west, is a narrow, largely arid region except for in the valleys. The sierra (highlands) is the region of the Andes; it includes the highest mountain peak of the country. The third region is the selva (jungle), a wide expanse of flat terrain covered by the Amazon rainforest that extends east. More than half of Peru's area is located within this region. The Amazon basin is the source of the Amazon River, which at 6872 km, is the longest river in the world. Peru contains 4% of the planet's freshwater.