The Amazon River of South America is the largest river in the world by volume, with a total river flow greater than the next eight largest rivers combined. The Amazon, which has the largest drainage basin in the world, accounts for approximately one fifth of the world's total river flow . During the wet season parts of the Amazon exceed 190 kilometres (120 mi) in width. Because of its vast dimensions, it is sometimes called The River Sea. At no point is the Amazon crossed by bridges. This is not because of its huge dimensions; in fact, for most of its length, the Amazon's width is well within the capability of modern engineers to bridge. However, the bulk of the river flows through tropical rainforest, where there are few roads and even fewer cities, so there is no need for crossings.