[The Conversation Africa] Pollution has become a worrying threat to Nigeria's Osun River. The river supports millions of people who rely on the water for agriculture as well as industries. It is also an integral part of Nigeria's treasured Osun-Osogbo sacred grove, a UNESCO world heritage site. Emmanuel O. Akindele unpacks what's causing the pollution, what harm it's causing and what must change to preserve the river's biodiversity.