Conversation so far:
where does the niger river start and end
The Niger River begins in the Guinea Highlands in southeastern Guinea and ends into the Gulf of Guinea in the Atlantic Ocean.
how long is the niger river
The Niger River is 4,180 km (2,600 mi).
where is the niger river located
The Niger River is the principal river of West Africa.

Question: what is unique about the river
Self-contained rewrite: what is unique about the niger river