Johannesburg — THE filamentous algae grows so thick in the irrigation canals fed by the Loskop Dam that labourers regularly remove bakkie-loads of the slimy weed, which thrives in water polluted with phosphates. It costs farmers dearly, as it increases the pH of the water, reduces crop yields and can cut the capacity of irrigation systems by a fifth.
The algae is just one of the many troubles facing the Olifants River, one of the most heavily contaminated rivers in SA. The river's source lies in the Highveld grasslands, from whence it flows north across Mpumalanga to the Loskop Dam. From there, it flows through the Kruger Park to Mozambique, where it reaches the Indian Ocean north of Maputo at Xai-Xai.
The hardworking river provides water to mines, farms, factories, power generators, municipalities and rural communities - and they all pollute the water to some extent in return. But precisely what is going on in the river, who is to blame and how best to clean it up, is still up for debate.
Figuring out how to rehabilitate the Olifants River is critical, as it provides water to more than 200 dams. Loskop Dam alone supports fruit and vegetable farms that employ 30000 people and have a combined European export market of about R1,5bn, according to Transvaal Agricultural Union vice- president Louis Meintjies.
Farmers are deeply worried: if the water is not cleaned up - and soon - their produce may no longer meet the grade for export, he says. Farmers hope to get some answers from a study commissioned from the Council for Scientific and Industrial Research (CSIR) by the Olifants River Forum, which counts farmers, mining companies, scientists, Eskom and environmental consultants among its members.
The study was prompted after a large die-off of fish in the Loskop Dam in 2007. "It meant something drastic was going on," says the forum's chairman, Dr Vik Cogho, the health and safety director for mining company Optimum Coal. There were also mass deaths among crocodiles in the dam and in the Kruger Park. Both the fish and the crocodiles died from a gruesome condition called pansteatitis, in which their body fat hardens and they gradually lose the ability to move, so they starve to death.
The crocodile population in the dam has plunged from 80 to three in the past five years, while that of the Kruger Park has fallen from 1000 to just 347 in the past two years. Scientists believe the condition is caused by high nutrient concentrations in the water from agricultural fertilisers and untreated sewage, but still do not understand quite how they trigger pansteatitis.
Although various companies, particularly the mines, have previously studied aspects of the river's water quality, little of this research has been made public.
The CSIR study will be the most comprehensive to date, as it will consider the health of the entire ecosystem and how it affects the river's water quality, says lead researcher Dr Paul Oberholster.
For the first time, scientists are considering how atmospheric conditions may be involved and hunting for signs of genetic mutations in plants and animals living in and around the river.
The aim is to generate a snapshot of the river's health, including pollution hotspots and the sources of their contamination, against which remediation efforts can be measured.
"We need to target the pollution at its sources, whether it's heavy metals, acid mine water or untreated sewage," says Mr Meintjies. "And we need scientific evidence that we can put on the table (to) get the government to apply the (law)," he says, referring to the legal principle of "polluter pays".
Sampling from the upper Olifants River, its tributaries the Klip and Wilge rivers, and the Loskop Dam began in November. The summary of the team's preliminary report makes for disturbing reading. The full version is being peer- reviewed, but the broad findings are unlikely to be challenged, Dr Oberholster says.
One of the worst sites sampled was a stream at Ferrobank, just outside Witbank, where scientists could find no signs of life. Instead they found "exceptionally high" levels of sulphates, iron, manganese, zinc, copper, vanadium, magnesium and aluminium, and a low pH (meaning the water is acidic). Little wonder that Daphnia pulex water fleas died when they were exposed to samples taken from the stream.
Sites along the main Olifants River were relatively less contaminated with heavy metals, with the water generally improving towards the Loskop Dam.
Nevertheless, the dam itself is in a bad way and is well on its way to becoming eutrophic, so rich with nutrients from agricultural run-off and poorly treated sewage that little but algae can thrive.
The researchers found microbial contamination at all the sites they sampled, most likely from poorly treated sewage flowing into rivers and streams, which poses a health hazard to people who draw water directly from the Olifants River and its tributaries.
The levels of Escherichia coli, an indicator of fecal matter in the water, exceeded local guidelines.
Rehabilitating rivers and dams is a slow process, and it needs to begin as soon as possible, warns Dr Oberholster. "Lake Washington took 30 years to become clean, but SA doesn't have enough water to wait that long."