A more thorough explanation:

Definition: Headwater refers to the beginning or source of a river or stream. It is usually the uppermost part of a river or stream that is closest to its origin.

Example: The headwaters of the Mississippi River are located in Lake Itasca, Minnesota. This is where the river begins and starts to flow southward towards the Gulf of Mexico.

Explanation: The example illustrates the definition of headwater by showing the starting point of the Mississippi River. Lake Itasca is the uppermost part of the river and is considered the headwater because it is the closest point to the river's origin. From there, the river flows downstream towards its mouth.