Pondweed harvesting should reduce pollution in Rietvlei Wetland Reserve

Weeds, rudders and boat propellers are generally regarded as a bad combination by recreational water users.

However, they find themselves on the same team at the troubled Rietvlei Wetland Reserve in Cape Town, where the city is using pondweed to tackle a water-pollution problem.

Rietvlei is inside the Table Bay Nature Reserve — between the suburbs of Milnerton and Table View — and has been plagued by pollution inflows. Specialist consultants called in by the city to address the problem have identified mechanical and manual harvesting of pondweed as the most efficient way of improving the water quality.

Pondweed, which absorbs nutrients such as phosphorous, can be grown and sustainably harvested using mechanical weed harvesters. In this way, harmful pollutants are removed from the aquatic system.

The move is one of several recommended interventions for Rietvlei. Others include using sewage grinders to prevent breakdowns and overflows at pump stations, and better monitoring of malfunctioning manhole covers.  

A new weed-harvesting boat is expected to be delivered by mid-January 2024.

Cape Town deputy mayor Eddie Andrews said the specialist report showed the harvester would be more effective than dredging. He said the city would manage pondweed growth “by reducing it in areas where recreational activities take place, while allowing it to expand in other sections”.

Less weed-propeller incidents, in other words.  

“The mechanical weed harvester will help us to undertake frequent, effective and controlled pondweed management. This is a priority for the city, as are interventions to reduce the inflow of nutrients and contaminants from the catchment feeding Rietvlei,” Andrews said.

Cape Town recently also approved a new mechanical weed harvester for Zandvlei.

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