Peru covers 1,285,216 km2 (496,225 sq mi) of western South America. 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; they define the three regions traditionally used to describe the country geographically. The costa (coast), to the west, is a narrow plain, largely arid except for valleys created by seasonal rivers. The sierra (highlands) is the region of the Andes; it includes the Altiplano plateau as well as the highest peak of the country, the 6,768 m (22,205 ft) Huascarán. The third region is the selva (jungle), a wide expanse of flat terrain covered by the Amazon rainforest that extends east. Almost 60 percent of the country's area is located within this region.
Most Peruvian rivers originate in the peaks of the Andes and drain into one of three basins. Those that drain toward the Pacific Ocean are steep and short, flowing only intermittently. Tributaries of the Amazon River have a much larger flow, and are longer and less steep once they exit the sierra. Rivers that drain into Lake Titicaca are generally short and have a large flow. Peru's longest rivers are the Ucayali, the Marañón, the Putumayo, the Yavarí, the Huallaga, the Urubamba, the Mantaro, and the Amazon.
The largest lake in Peru, Lake Titicaca between Peru and Bolivia high in the Andes, is also the largest of South America. The largest reservoirs, all in the coastal region of Peru, are the Poechos, Tinajones, San Lorenzo, and El Fraile reservoirs.
The combination of tropical latitude, mountain ranges, topography variations, and two ocean currents (Humboldt and El Niño) gives Peru a large diversity of climates. The coastal region has moderate temperatures, low precipitations, and high humidity, except for its warmer, wetter northern reaches. In the mountain region, rain is frequent in summer, and temperature and humidity diminish with altitude up to the frozen peaks of the Andes. The Peruvian Amazon is characterized by heavy rainfall and high temperatures, except for its southernmost part, which has cold winters and seasonal rainfall.
Because of its varied geography and climate, Peru has a high biodiversity with 21,462 species of plants and animals reported as of 2003, 5,855 of them endemic. Peru has over 1,800 species of birds (120 endemic), and 500 species of mammals and over 300 species of reptiles. The hundreds of mammals include rare species like the puma, jaguar and spectacled bear. The Birds of Peru produce large amounts of guano, an economically important export. The Pacific holds large quantities of sea bass, flounder, anchovies, tuna, crustaceans, and shellfish, and is home to many sharks, sperm whales, and whales.
Peru also has an equally diverse flora. The coastal deserts produce little more than cacti, apart from hilly fog oases and river valleys that contain unique plant life. The Highlands above the tree-line known as puna is home to bushes, cactus, drought-resistant plants such as ichu, and the largest species of bromeliad – the spectacular Puya raimondii.
The cloud-forest slopes of the Andes sustain moss, orchids, and bromeliads, and the Amazon rainforest is known for its variety of trees and canopy plants.