Xanthea Limberg, mayoral committee member for water and waste
Referring to “Sewage spills threat to vlei”, test results showed unacceptable levels of E.coli recorded at test sites in the northern part of the vlei, and along the Big Lotus Canal.
Samples from the rest of the vlei did not show signs of sewage contamination.
The first incident was reported on August 26 and the second incident was reported on September 17.
Pollution of this river is an ongoing challenge due to levels of illegal and informal development along the river, as well as intensive abuse/misuse of sewers in the catchment.
Because of the chronic pollution, the City has installed a low-flow diversion before the river meets Zeekoevlei to channel a limited amount of contaminated stormwater to the sewerage system before it reaches the nature reserve.
However, strong flows in the river (for instance during rain) are too much for sewers to accommodate so pollution to the vlei will increase.
Each of the incidents listed above, which reported pollution flowing into the vlei, triggered multi-pronged investigations. Our sewer reticulation team did not find evidence of a pump station failure or a specific blockage/overflow that caused the public to complain, but did find that the diversion chamber had been vandalised.
As such recent complaints were likely a result of a combination of higher rainfall and the damage to our low-flow diversion chamber.
Big Lotus River is an ongoing challenge, however, the most recent reports were likely linked to a combination of wet weather and the vandalised low-flow diversion chamber detailed in the media release below.
Regarding the previous investigation, a source could not be easily identified. The City is, however, sustaining infrastructure maintenance operations, and will continue to clear sewer blockages as they are reported. When reports of pollution are received, the City will always investigate and attempt to address all possible sources.
The increased presence of biodegradable organic matter such as sewage provides nutrients (i.e. nitrates and phosphates) that encourage the growth of bacteria and micro-organisms (eutrophication) which depletes the oxygen levels in water ( causing anaerobic conditions).
In Cape Town, the eutrophication of our watercourses has in the past caused algal blooms which could be toxic to plants and animals.
The reserve was partially opened on Friday October 9, however, water users have been advised to avoid the northern area of the vlei.