I have heard that rivers form from meltwater and rainwater flowing down mountains. But I know that not all rivers start near mountains. As an example the Mississippi river doesn't start near any mountains. Rather it starts at Lake Itasca which is surrounded by taiga(coniferous forest). This lake itself has water coming into it from Nicollet Creek and the Elk Lake outlet stream. Nobody knows if Nicollet Creek starts near mountains or not. But even if people did know that, it still wouldn't mean that the Mississippi River originated in mountains. So no, not all rivers form from mountains. Excessive rainfall in the long term in any area of land can form rivers. As an example: Suppose Person A survives in the wild for years and more south winds than usual brings more rain to the area where Person A is. Over years, this becomes the norm and soil starts to erode but during the winter there is ice in the depressions in the soil. Once it warms up more soil erodes to a point that after several decades a body of water has formed. This eventually becomes a river. So why do people often say that rivers form from mountains when that isn't always the case? And what determines whether the body of water that forms is a lake, river, or other body of water? Water speed? Amount of water over time?