The United Nations' Environment Programme has completed an extensive study on oil pollution in the Niger Delta. The UN says that many of the region's marshes, creeks and rivers are covered with more than a centimetre of oil. The land is polluted up to one metre deep in other areas. The drinking water is unsafe or toxic.

The UN is calling for a massive clean-up operation in the Delta. It's expected to take 30 years and will cost billions of euros.