A week after the Cradle of Humankind made global headlines for the discovery of a new species, Homo naledi, top scientists are raising a stink over sewage and toxic water leaking into the world-famous fossil site. They say South Africa urgently needs to clean up its act in case the water starts eating away at the country's underground heritage - much of which has yet to be discovered.Their fears have partly been confirmed by a new Cradle of Humankind water-monitoring report that suggests the incoming tide of human effluent and acid mine water appears to be here to stay - and in some cases is getting worse."Where there is something wrong we have to clean it up," said Bruce Rubidge, director of the Evolutionary Studies Institute at the University of the Witwatersrand.story_article_left1"We don't know what the effect [of polluted water] is, but it probably can't be good. We have to realise that this is a world heritage site which has a record of early human ancestry," Rubidge said.The latest Cradle of Humankind water-monitoring report for the period April 2014 to May 2015, conducted by the Council for Scientific and Industrial Research, draws attention to both acid mine water and "unacceptably high levels" of bacteria related to human waste in the lower reaches of the Bloubank River that flows underground just upstream from the Cradle of Humankind.The report blames the Percy Stewart Wastewater Treatment Works run by the Mogale City Municipality.The report says: "The results indicate severe non-conformance of faecal coliforms (and therefore almost certainly also of E Coli) in regard to potable, animal and recreational use ..."This situation undoubtedly worsens progressively with distance upstream."Patrick Randolph-Quinney, head of the Human Identification Unit at the Wits School of Anatomical Sciences, said: "This is a big, big issue. There is precipitated calcium carbonate in these caves, and that is dissolved by acid water. It is potentially damaging irreplaceable fossil sites. Nothing good is going to come out of this."Randolph-Quinney said Makapans Valley world heritage site in Limpopo faced a similar threat due to mining activity and polluted surface runoff from tailings dams.Fossilised remains of about 15 "proto-humans" - presented to the world last week as a new species dubbed H. naledi - were recently excavated from a rock chamber deep inside the Rising Star cave complex in the Cradle of Humankind.story_article_right2The site is just a kilometre or two from the Sterkfontein cave site, which is in an area of high "hydro-vulnerability".Mogale City Municipality did not respond to Sunday Times queries this week.Although the government has set up an emergency treatment plant near Randfontein to partially treat about 30million litres of mine water a day, more than twice that volume of water gushed out of the ground during heavy rainfall periods.As a result, a large amount of untreated mine water entered the groundwater system last year, the report found.Fortunately, the acid water had been largely diluted by unpolluted spring water and recent measurements showed a marked improvement in levels of mine water discharge - thanks to below-average rainfall last summer.Craig Sheridan of Wits's Industrial and Mining Water Research Unit said the impact of polluted water needed to be assessed. "If the fossils are liable to dissolve, then that's a big deal," Sheridan said, adding the presence of uranium was another key concern."Uranium is normally shielded by normal rock around it, but then the water starts to dissolve uranium."The second that it is mobile, it is an issue," he said...