Zandvlei Trust

Water Quality in the Westlake Wetlands 
(Extract article from the 1993 Autumn Newsletter)

Concerned members have noted a progressive increase in coverage of waterweed in the above area over the past 3 to 5 years. Normally one associates the proliferation of plant material in disturbed water bodies with increased nutrient loading which so often accompanies urbanisation and an increase in environmentally unfriendly human activities such as over fertilzing lawsns, disposal of dog faeces down the gutter etc.

However, some members of the CTCC(Cape Town City Council) Engineer's Dept maintain that water quality has actually improved over this period. Unfortunately it is difficult to argue the point as we have limited accesses to equipment and expertise to do analyses ourselves and also struggle to get hold of CTCC's reports on the water quality of the system.

In a snap survey, followed by laboratory analysis of samples we have been able to show;

  • that intermitttent overflow of sewerage from the pipe alongside the Westlake Stream upstream of the Blue Route (inside Pollsmor Prison) has led to nutrient loading of this already overgrown river and
  • that the dissolved oxygen in dead end areas of the Westlake Wetlands is so low that there are high levels of hydrogen sulphide present - this gas is known to be toxic to most fish, birds and humans.

However all is not doom and gloom and thanks largely to the efforts of one of our members Bobsie Sacks we were able to get the City Council to get one of the weed harvesters over to this side of the vlei and for once to make an impact on the infestation of alien waterweed (Hornwort, Parrots feather and Water Hyacinth) choking the Westlake Wetlands. Numerous attempts to do the same by hand by members have failed and in fact we had a Saturday afternoon effort by members, Sea Cadets and other public minded friends just the week before the harvester arrived. All the hype in the media about this might have also have helped sway the Council. This was no easy task after years of excuses why this could not be done before, is tribute to both Mrs Sacks and the pragmatic approach of the new Parks and Forests deputy Mr Coetzee.


"Kingfisher" waterweed harvester in operation at Zandvlei.

Another positive development resulting from a 50/50 TV production and follow up by energetic Bobsie Sacks is the possibility of obtaining a consignment of triploid (sterile) grass eating Carp from the Rand Afrikaaans University. These fish eat their own body weight in waterweed each day once they attain 1kg, and our name is on the list of customers for next year.
All we need now, is permission from Cape Nature Conservation and R7500 from donors and Zandvlei can join the list of water bodies cleared of waterweed by this marvel of nature.

Geoff Bailey

                                                                                                  

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