A river is a natural watercourse, typically flowing towards an ocean, sea, or lake. It is formed from precipitation, melting snow, or springs, and is characterized by its flowing water. Rivers can vary in size, length, and depth, and they often have tributaries, which are smaller streams that feed into them. Rivers play a crucial role in the ecosystem, providing habitats for various wildlife and plants. They also serve as important resources for human activities, such as drinking water, irrigation for agriculture, and transportation. Notable rivers include the Amazon, Nile, and Mississippi.