(IDEX Online) - Divers who scan the shallow sea floor off South Africa's western coast for diamonds claim an industrial mining operation is muddying their waters and causing long-term damage.They've complained to environmental inspectors about a series of coffer dams - temporary sea walls built by diamond mining companies so they can pump out water and sift the gravel for gems.The country's Environmental Management Inspectorate, also known as Green Scorpions, is investigating their claims that sediment dumped at the mouth of the Orange River is smothering the seabed, damaging the inshore reef systems, and wrecking their livelihoods.Veteran diver Kobus Kriel told the South African news agency GroundUp the sea was so dark with sediment "we can't even dive with lights".Diamond mining is managed by the Alexkor Richtersveld Mining Company Pooling and Sharing Joint Venture (PSJV), in which the government-owned diamond mining entity Alexkor has a 51 per cent stake. The community of the Richtersveld municipality owns the remainder.GroundUp said the mining company had not responded to its inquiries.Pic from GoogleEarth shows coffer dam mining operations in 2017