The naturally flowing single stream of water on the surface of earth is called river. Rivers always follow the slope. Rivers usually originate from high mountain areas. Those rivers which have their origin on very high mountains, get water from rainfall as well as from the melting snow. These rivers continuously flow all the year round and are called perennial rivers, such as the Ganga and the Yamuna. Some rivers flow only in the rainy season. These are called seasonal rivers. The Luni river in Rajasthan is an example of seasonal river.
