A region of Nigeria’s oil-rich southern delta has suffered widespread ecological damage from spilled oil seeping into its drinking water, destroying plants and lingering in the ground for decades at a time, according to a U.N. report released Thursday.

The report, issued by the United Nations Environment Program, said it will take up to 30 years to clean the oil-stained Ogoniland area within Nigeria’s Niger Delta, a sprawling region of swamps, mangroves and creeks. The world body suggested that the Nigerian government and the oil industry set up an initial $1 billion trust fund for the cleanup.

However, environmental cleanup remains an afterthought in Africa’s most populous nation as oil revenue funds a bloated and corrupt government dependent on production. Cleaning up the Ogoni area — more than 600 square miles — would be a challenge for any government, the U.N. body acknowledged.

“The environmental restoration of Ogoniland could prove to be the world’s most wide-ranging and long-term oil cleanup exercise ever undertaken if contaminated drinking water, land, creeks and important ecosystems such as mangroves are to be brought back to full, productive health,” the body said in a statement.

Although oil production in Ogoniland stopped in 1993, pipelines and flow stations operated by a subsidiary of Royal Dutch Shell and the state-run Nigerian National Petroleum Corp. still run through villages and fields.

Oil spills from those sites, caused by aging pipelines and vandalism, have thoroughly damaged lands, the United Nations found. In one case, investigators found a village where drinking water contained benzene levels that were 900 times the international limit. They also found one area where an oil spill 40 years ago had still not been cleaned up.

“The Ogoni people live with this pollution every minute of every day, 365 days a year,” the report said. “Since average life expectancy in Nigeria is less than 50 years, it is a fair assumption that most members of the current Ogoniland community have lived with chronic oil pollution throughout their lives.”

Shell helped fund the U.N. investigation, prompting criticism by some environmentalists that the report would not take on the oil giant. The report said damage can be caused by failing oil pipelines, as well as by thieves who tap into the lines to steal crude oil. It also said U.N. officials saw such theft during the day in the Ogoniland area and suggested that there could be “collusion” with government officials.

Nigeria, a member of the Organization of the Petroleum Exporting Countries, is one of the top suppliers of crude oil to the United States.

— Associated Press