Water pollution allegedly caused by mining companies has sparked a probe by the anti-corruption ombud.

Scientists have found high quantities of uranium, sulfuric acid and other toxic materials in streams and rivers in and around Johannesburg, Bloomberg reported. Farmers have also complained about pollution from coal mines in Mpumalanga.

Oupa Segalwe, spokesperson for the public prosecutor, told Bloomberg that the inquiry by the public protector is at an early stage. “The investigation has to do with alleged pollution of water as a result of mining operations in a number of provinces,” he said.

The Federation for a Sustainable Environment (FSE) chief executive Mariette Liefferink told Bloomberg that the public protector contacted the FSE after the environmental lobby group laid a criminal complaint against the directors of mining companies including AngloGold, Exxaro Resources and Glencore Xstrata. FSE says the department of water affairs allegedly failed to enforce environmental regulations.

“It’s extremely encouraging and heartening that the public protector approached us about this issue,” said Liefferink.