Oil represents 95 percent of Sudan's exports and is both a source of huge tension between between Khartoum and the semi-autonomous south and the last thing forcing the former civil war foes to work together.

In the central Unity state, one of southern Sudan's main oil-producing regions, the German NGO Sign of Hope has led a fact-finding mission which revealed alarming pollution levels.

"Oil exploration and exploitation in the oilfields of Mala and Thar Jath pose serious threats to human beings, livestock and the environment," Klaus Stieglitz told AFP.

Pointing to the Thar Jath central processing facility (CPF), the NGO's vice chairman explained water flowing off the huge installation is a major source of contamination.

"Waters found in drilling pits at oil wells are another major source of contamination. Contaminants of both sources have already reached the drinking water layers," he explained.

Stieglitz cited the case of Rier, a village in Unity state close to the CPF, where concentrations of salts and contaminants like cyanides, lead, nickel, cadmium and arsenic had reached critical levels.

"The contamination has got a serious impact on the daily life of the local population. In the village of Rier the inhabitants do not use the water coming from their boreholes," he explained.

"Locals who drink this kind of water can get diarrhea and a subsequent dehydration of the body which might lead to death if untreated," Stieglitz said.

"The heavy metal concentrations of these waters will have negative impact on the health situation of the some 300,000 inhabitants of the affected area which covers 4,000 square kilometres (1,500 square miles)," he added.

Stieglitz urged the facility's operator WNPOC, a subsidiary of Malaysian giant Petronas, to treat the plant's water adequately and prevent seepage.

"To secure public health the government must also improve the quality of drinking water dramatically and at the same time prevent an ecological catastrophe," he added.

The pollution caused by the oil industry is also threatening the Sudd tropical wetlands, which cover an area of 30,000 kilometres (11,500 square miles).

The swamps, flood plains and grasslands support a rich animal diversity including hundreds of thousands of migratory birds and are inhabited by the Nuer, one of southern Sudan's two main tribes.

More than two decades of north-south civil conflict had incidentally protected the site through isolation but the intensification of oil activities since the 2005 peace deal is now a threat.

In 2006, the Sudd wetlands were certified of international importance under the Ramsar convention.

Many in southern Sudan, one of the most remote and impenetrable regions on the continent, feel that the oil riches discovered in the early 70s never turned out as the blessing it promised to be.

Sudan's oil is mostly found in the south and sold by the north, leaving many southerners feeling that they got the rough end of the stick.

"I see nothing coming out of the oil," said Reverend Roko Taban Mousa, an influential cleric in the oil-producing regions of Unity, Upper Nile and Jonglei.

"In the north, where the oil is going and the refineries are, there is an economic boom. But the production areas which should have benefited first have no services, no development. There is nothing and on the contrary, things have got worse," he told AFP.

"Oil could have been a blessing for southern Sudan had it been used properly, first for the development of the area where petrol is produced, and then the rest of the country, but it's exactly the contrary that is happening."

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