A river source is the starting point of a river, where it begins its journey. This source can be found in various locations, such as mountains, hills, or springs. The water may come from melting snow, rainfall, or underground aquifers, and it flows downhill due to gravity, eventually forming a river. As the river flows from its source, it travels through different landscapes, collecting water from tributaries and streams along the way. The characteristics of the river can change based on its source, affecting its speed, width, and the ecosystems it supports, including plants and animals like fish and birds.