Dam |
Cyanobacterial count (cells/ml) (including Anabeana, Arthrospira, Cylindrospermopsis, Lyngbya, Merismopedia, Microcystis and Oscillatoria |
Hartbeespoort |
22 342 |
Vaal |
33 524 |
Spitskop |
7 851 |
Koppies |
Not available |
2. Results can be provided for all the dams since 2011 as requested, except Barberspan and Chrissiesmeer. The data information can be viewed on the Directorate’s website - https://www.dwa.gov.za/iwqs.
3. Addressing cyanobacteria in dams requires a multidisciplinary approach with its foundation in catchment management. Nutrient loading resulting from run-off in catchment where the dam is located, is the main reason for cyanobacterial blooms.
This loading takes place as a result of, inter alia, overloaded and / or dysfunctional waste water treatment works and agricultural run-off. DWS addresses this through collaboration with and guidance to local authorities, whom is responsible for operating these waste water treatment works. The Green Drop project is an example of this, where the efficient operation of wastewater treatment works by municipalities is audited and scored. Based on the outcome of this evaluation, guidance is provided by the Department of Water and Sanitation (DWS) to municipalities to assist them with adhering to the license conditions of the waste water treatment works.
The DWS has also recently acquired the services of Cuban engineers to assist local municipalities with the improved operation of their waste water treatment works.
The Department developed a set of guidelines for eutrophication management, including best agricultural practices which, if implemented by farmers, will reduce the nutrient loading resulting from agricultural run-off.
A specific project on the Hartbeespoort Dam to address the water quality remediation, which includes the treatment of cyanobacterial blooms, is the Metsi a Me project. This is a multidisciplinary project which addresses the remediation of dam specific water quality.
There is currently no similar scale projects on the other dams mentioned in the question, as these dams’ issues are addressed on a catchment base.
(4) Cyanobacteria, when present in high numbers in the water column, and under conducive environmental conditions, can release a toxin, microcystin, which could pose a health risk if untreated water is consumed by humans and animals. In addition, when the algal blooms die off and decompose, it can result in unpleasant smells, impacting on recreational users.
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