The southern Nigerian city of Port Harcourt lies at the mouth of the river Niger.
It has long suffered from pollution from oil spills, but now plastic too is a growing problem.
It clogs the city’s waterways, killing marine life and endangering the livelihood of the local fishing population.
According to researchers, 10 rivers are responsible for depositing 90% of the plastic that ends up in the sea. Eight of them are in Asia and two in Africa: the river Nile and the river Niger.
The BBC’s Mayeni Jones went to what was once known as the Garden City of Nigeria, to find out what’s causing the problem and to meet some of the people fighting back.
Video journalist: Joe Inwood
Plastic pollution blights Nigerian city Port Harcourt