(IDEX Online) - Diamond miners in Lesotho have been accused of polluting rivers in the landlocked kingdom.The royalties it receives from South Africa for water far outweigh its annual diamond revenue. (Forecast at $70m compared to $12.7bn for the current financial year).But a confidential report reveals harmful levels of toxic mining effluent in rivers that feed the Lesotho Highlands Water Project (pictured), according to the country's MNN Centre for Investigative Journalism.The report identifies the culprits as Letseng Diamond Mine (jointly owned by Gem Diamonds and the Kingdom of Lesotho), the Kao mine (Storm Mountain Diamonds, jointly owned by Namakwa Diamonds Limited and the Kingdom of Lesotho) and the Liqhobong Diamond Mine (jointly owned by Firestone Diamonds and the Kingdom of Lesotho).The MNN report, Lesotho's Dangerous Water Gamble, claims they continue to pollute water sources critical to the project with nitrate contamination, despite repeated promises to the contrary.It quotes a report by the Lesotho Highlands Development Agency, which says: "Although mines have promised to address these issues, the level of nitrate pollution remains the same." The three mines responded to the MNN report. Letseng said: "The most recent independent water quality assessment conducted through an accredited laboratory, confirmed that nitrate levels in the Khubelu surface water sources at the downstream communities of Patising and Maloraneng have consistently been within the drinking water standards including over the October 2021-April 2022 period mentioned in media reports." Kao said: "The nitrate levels measured at the sampling sites are largely under the required threshold. SMD [Kao mine] uses ammonium nitrate-based explosives in the pit for blasting. The nitrates therefore build up over time and are in excess in the vicinity of the mine."Liqhobong said: "Regular tests are conducted on water, air and noise pollution to ensure that all disturbances are within acceptable limits. Any deviations are identified and corrective action is taken immediately."