It is where it starts.
River
The main parts of a river system include the source (where the river begins), the course (the path the river takes), the mouth (where the river empties into a larger body of water), tributaries (smaller rivers or streams that flow into the main river), and the watershed (the area of land that drains into the river).
The Nile River and its tributaries which was the source of their food and basis of their transport.
calorado river
The melting waters are the main source of the Nubra River, which drains into the Shyok River.
Clutha River ,Otago, New Zealand
an oxbow lake can form
main source for food and water
Mesopotamia.
I believe the water source for Egypt and Sudan is the Nile River.
The Andes mountain streams
No it is Mississippi