We see that the water in streams and rivers always rushes to the sea. Why does the river always flow? Where did it come from?

From water vapor. What you see is just a cycle. In the process of flowing, water begins to slowly evaporate and become gas under the action of sunlight. Under the action of ocean current or monsoon, gas begins to flow, turns into clouds in the air, and the clouds turn into rain and fall. On the surface, a tree is equivalent to a big reservoir. It flows out bit by bit and becomes a river, a river, ... Hehe, it's not very expressive, but it's probably like this ~