Hello Becky, they flow because of gravity: they go from the higher point to the lower point. Typically rivers begin in high mountains as torrents, going downhill they meet a lake or a bigger river. This water flows until it reaches the sea. Exceptions might be when you have regions of land below the sea level like some parts of Holland and water can get trapped.
Gravity! That’s the key to it. The same way everything falls towards earth, so rivers flow to their lowest point, usually the sea. This why they flow down mountains and across plains with a tiny slope.
Lakes don’t always flow though. Some are “stagnant”, such as lakes high up in mountains or beside the sea.
Hi Becky, great question! Rivers always flow downhill… a stream or river is formed whenever water moves downhill from one place to another. For example, most rivers begin high up in the mountains, where snow (during winter or from ancient glaciers) is melting and these rivers also collect water on their way down to the sea. They collect water from rain, and from other streams that meet up with each other. In lower places where there’s no mountain peaks, rivers here start from springs, which is water that seeps from to the surface from the ground. It may form a lake or pool or may start running downhill, forming a flowing river! Lakes are a totally different story. They are mostly still, but sometimes you ll find some that have currents. This is mostly caused by wind, changes in water density, and inflow or outflow of water from the lake. Wind drags air over the surface thus causing it to move, in the form of waves. How do changes in water density cause currents? well, changes in temperature cause the water to rise or fall. Hope that helps to answer your question!