Why do oceans have salt water but rivers have fresh water?
The water in rivers comes from rain. Rainwater does not have any salt in it. The river picks up a small amount of salt from the ground as it travels downhill. The salt enters the ocean at the river's mouth. The saltwater mixture becomes saltier as water evaporates.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.
### Instruction: Why do oceans have salt water but rivers have fresh water?
### Input: 
### Response: The water in rivers comes from rain. Rainwater does not have any salt in it. The river picks up a small amount of salt from the ground as it travels downhill. The salt enters the ocean at the river's mouth. The saltwater mixture becomes saltier as water evaporates.