A river is a natural waterway, which moves water diagonally the land from upper to lower elevations, and is a main part of the water cycle. The water within a river is generally from rain through surface runoff and release of stored water in natural reservoirs, such as groundwater.
The beginning of a mountain river from their resource, all rivers run downhill, naturally terminating in the sea or in a lake, during a flowing together. In dry areas rivers sometimes finish by losing water to evaporation. River water may also gain access to the soil or pervious rock, where it becomes groundwater. Extreme abstraction of water for use in industry, irrigation, etc., can also source a river to dry before reaching its natural boundary.