What is the fine-grained topic of the following text: The active basin is shared by nine African states (Benin, Burkina Faso, Cameroon, Ivory Coast, Guinee, Mali, Niger, Nigeria and Chad) and the river plays a key role in the region in terms of food production, preserving biodiversity and as a barrier to desert encroachment. Only return the topic.
The active basin's role and its sharing by nine African states