Royal Dutch Shell is facing opposition to its plans to seek shale gas in South Africa's semi-desert Karoo region, as farmers fear methods used to extract it will contaminate water and harm the environment.

The outcome of whether Shell is allowed to proceed could affect prospects for other oil and gas companies in the Karoo, which may hold substantial deposits of gas in shale.

This gas can now be exploited due to new techniques and could bring a much needed fresh source of energy to Africa's largest economy, which is heavily reliant on coal.

Petrochemicals group Sasol, Anglo American, Falcon Oil and Gas, and Bundu Gas and Oil Exploration, are among those eyeing shale gas in the region.

Public concern focuses on the extraction method known as hydraulic fracturing or fracking, in which drillers blast millions of litres of water, sand and chemicals at high pressure in underground rock formations to create cracks for gas and oil to escape easier.

We are very concerned about the environmental impact, especially because fracking is not regulated in South Africa, Derek Light, a lawyer representing a number of Karoo land owners and interested parties told Reuters on Thursday.

He said farmers were worried about the sensitivity of the underground water systems upon which the Karoo is totally dependent, should contamination occur.

According to findings from a U.S. Congressional probe released on Monday, several energy companies there may have violated environmental rules by injecting diesel into the ground without permits as part of the controversial drilling technique.

We've got some serious concerns about fracking, it is as yet an unproven technology with unacceptable risks for fresh water abstraction and pollution, said Mark Botha, head of conservation at environmental group WWF South Africa.

Oil major Shell, which has held public consultations as part of its environmental impact assessment, said in January it had applied to Petroleum Agency South Africa for exploration rights in the Karoo.

Fracking is the best method to extract gas that is trapped in shale, Phaldie Kalam, vice president communications for Shell Africa told Reuters.

He said Shell noted the public's concerns and would incorporate that into an environmental management plan currently under design, the final version to be handed in by end-April.

Minister of Mineral Resources Susan Shabangu on Tuesday placed an indefinite moratorium on the processing of all new exploration and production rights in the Karoo, although this would not affect those applications already in the pipeline.

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