A faulty pipe from an offshore oil field run by Royal Dutch Shell near Nigeria’s coast spewed crude oil into the ocean for up to 25 hours as workers loaded a waiting tanker, the company has admitted.

While Shell continues to investigate the cause of what is probably the worst offshore spill in more than a decade near oil-rich Nigeria, the nation’s beleaguered government remains largely reliant on the oil firm to clean up the spill.

While the huge slick remains offshore, it still poses a danger to wildlife and plants in a region where spills already stain the environment.

The spill happened at the Bonga offshore oil field, about 75 miles off Nigeria’s coast. The field, which Shell operates in partnership with Italy’s Eni SpA, Exxon Mobil, France’s Total and the state-run Nigerian National Petroleum is controlled from a large ship as opposed to a stationary rig.