The Amazon River of South America is the world's largest river and the lifeblood of the world's largest ecosystem, spanning two-fifths of an entire continent. It is home to a huge variety of animals and plants that dwell in its lush, evergreen environment. It is the mightiest river in the world by volume, with six times greater total river flow than the next six largest rivers combined, and the most extensive drainage basin in the world. Because of its vast dimensions it is sometimes called The River Sea. Running about 4,000 miles (6,400 kilometers), most sources regard the Amazon as the second longest river in length, compared to Africa's Nile River, though this is a matter of some dispute.