From: Peter Arderne <>
Date: Sat, 6 May 2006 13:19:46 -0000

Subject: Fish Kills in the Vaal

Dear All,
following the recent Yellowfish Working Group conference we sent press releases and pics to the media including most of the daily newspapers. The press release sent to the newspapers was based on the excellent report prepared by Dr Steve Mitchell which summarised the panel discussion on the Friday evening. I have attached it again plus a pic submitted by Johan Hardy of a fish kill in one of the tributary rivers in the Free State. This kill was actually a result of a fertilizer spill but we have a number of other dramatic photos of kills resulting from sewerage discharge. We suggest that you distribute this material as widely as possible in order to keep the public’s attention focussed on the problem. As we know the problem is not only limited to fish and other aquatic life but it has become a very real threat to human health.


Why the fish kills in the Vaal?

During the early part of 2006 there were extensive fish kills in and downstream of the Vaal Barrage. These attracted a substantial amount of negative press but the main question, ‘what caused these fishkills?’, remained unanswered. It took a meeting of a multidisciplinary group of experts to provide the answer. These experts met at the 10th Yellowfish Working Group Conference in April at Sterkfontein Dam outside Harrismith
The Vaal catchment provides water for and receives waste from a large domestic and industrial area centred on the Ekurhuleni Metropolitan Area, and the population serviced by the river is increasing both as a result of migration into the area and from the increased number of people provided with services. Routine monitoring shows that there is a very heavy nutrient load being discharged into the tributaries of the Vaal, particularly via the Klip River. This makes the river highly eutrophic. Under current management the system is reasonably stable, although the reduced biodiversity shows that it is overloaded. The destabilisation of the system, which occurred in early 2006, came from two separate sources both of which are related to sewage, a situation exacerbated by the lack of adequately trained personnel to manage many of the smaller works. Sewage has a high oxygen demand, and sewage works are designed to treat this. One malfunction that happens on a routine basis is that sewers are deliberately caused to overflow to provide gardeners with water to cultivate market gardens, and the other is the exceptional rain that fell during the period. Blockage of sewers diverts the highly polluted sewage from works where it would be treated to non-point source run-off. This is added to the stormwater run-off during heavy rainfall, which has increased substantially with the growth of Ekurhuleni as the cities are estimated to have over 40% impermeable surfaces. In this case the more serious event was the ingress of large quantities of stormwater into the sewers. Modern sewage works are based on sensitive and closely controlled biotechnology. Storm water ingress can increase the hydraulic load by up to 200%, and this washes the activated sludge out of the works and so the sewage receives minimal treatment. Effectively, the works discharge untreated sewage. This ingress is largely a result of malfunctioning sewer systems through causes such as manhole covers being vandalised and a lack of maintenance in certain areas by the responsible authorities.
The middle Vaal is already a heavily used river. A slug of untreated sewage may not cause apparent harm while it is in a turbulent stretch of the river, but the moment this slug reaches a stretch of quieter flow the oxygen levels in the water will drop to a level too low to support fish life, and so the fish will die. Some species are more sensitive to low oxygen levels than others, and these more sensitive species will be the first to die.

Fish kills are spectacular, and attract a lot of attention. However, what many people do not see is the other dangers of such an incident. Untreated sewage carries a high concentration of disease organisms, and disease contracted through drinking contaminated water is one of the biggest causes of infant mortality worldwide. Recent epidemics of Cholera in KwaZuluNatal and Typhoid in Delmas bear witness to the danger of allowing water to become contaminated.

Fish kills are serious in themselves, but they should be seen as one of a range of symptoms affecting not only the health of our rivers, but the health of people dependant on the rivers for their livelihoods as well. Appropriate action should be taken to address the root cause.

Contact: Peter Arderne at email or 083 4577478