The Amazon River in South America is the largest river by discharge volume of water in the world, accounting for approximately 20% of the global riverine discharge to the ocean. It holds a massive drainage basin that covers nearly 40% of the South American continent. While there is a long-standing debate with the Nile regarding which is longer, the Amazon's sheer volume is undisputed; it carries more water than the next seven largest tropical rivers combined. During the wet season, parts of the river can exceed 190 kilometers in width. The river is the lifeblood of the Amazon Rainforest, the world's richest biological reservoir, containing millions of species of insects, plants, birds, and other forms of life, many of which are still unrecorded by modern science.