The Amazon carries more water than any other river in the world. The drainage basin is enormous (c.2,500,000 sq mi/6,475,000 sq km; c.35% of South America), gathering waters from both hemispheres and covering not only most of N Brazil but also parts of Bolivia, Peru, Ecuador, Colombia, and Venezuela. For most of its course the river has an average depth of c.150 ft (50 m). The gradient of the river is very low: Manaus, c.1,000 mi (1,610 km) upstream, is only c.100 ft (30 m) higher than Belém and is an ocean port; ships with a draft of 14 ft (4 m) can reach Iquitos, Peru, c.2,300 mi (3,700 km) from the sea. Peru, Ecuador, and Colombia have international shipping rights on the Amazon. In the lowlands stretching east from the Andes is the largest rain forest (selva) in the world—a wet, green land rich in plant life. The tropical climate is tempered by the heavy rainfall (exceeding 150 in./381 cm annually in parts of the upper and lower regions) and by high relative humidity; the average temperature at Santarém, 400 mi (644 km) upriver, is 78°F (26°C).