/ 13 November 2023

SA rivers, dams, used as waste disposal systems, says ecologist

Artificial lakes like Hartbeespoort must be treated and managed as semi-natural lake ecosystems to keep them healthy and support demands made on them such as raw potable water and recreational use. (Delwyn Verasamy/M&G)

Artificial lakes like Hartbeespoort must be treated and managed as semi-natural lake ecosystems to keep them healthy and support demands made on them such as raw potable water and recreational use.

This is according to Bill Harding, a consultant ecologist with PhDs in aquatic science and public law who specialises in water and public trust law.

He said that with minor exceptions, this is not the case in South Africa, especially in Gauteng and North West and to a degree in KwaZulu-Natal.

“Most regrettably, South African rivers are used as waste disposal systems via which wastewater effluents, principally urban sewage effluents, are conveyed to downstream reservoirs”, he said, adding that given the country’s arid circumstances, these effluent return flows are part of the water required for reuse.  

“This would all be absolutely fine if South African wastewaters were treated to appropriate levels, but they are not. The treatment requirements for nutrients in these effluents are shockingly inadequate, even were the general condition of so many treatment plants not as degraded as they have been allowed to become.”

Sentinel examples

The upshot of this is that many of the country’s reservoirs — “Hartbeespoort and Roodeplaat are sentinel examples” — serve as little more than maturation or oxidation pond extensions of the wastewater treatment plants discharging into their influent rivers.  

Harding said this is not a new realisation. “One of South Africa’s most perceptive aquatic ecologists, the diatomologist Bela Cholnoky, referred to Hartbeespoort as nothing more than an oxidation pond in 1958. It is, however, a fact that has been ignored for a very long time, to the nation’s collective detriment.”

He explained that the loads — the product of concentration and volume — of nutrients entering these reservoir waters “far exceed their capacity to assimilate them”.  

“The direct consequence is that the lake rapidly becomes nutrient enriched (eutrophic) and becomes prone to overgrowth by problem plants [for example water hyacinth] and noxious algae [for example toxic cyanobacteria].”  

Endemic problem

This has been the situation in Hartbeespoort since the 1960s and persists to this day. “When I first worked as a student at the CSIR [Council for Scientific and Industrial Research] in 1975-76, the water hyacinth in the Magalies River inlet stood a metre above the water surface and the algal scums had the consistency of glue.”

In most instances, there would need to be at least an 80% reduction of present loads and simply eradicating the symptoms — plant and algal growth.  

“The eutrophic status of such waters impacts negatively on the ecosystem health, water loss, recreational usability of the lake, as well as surrounding property values. The longer the impact persists, the greater will be the harm done to the already very limited ecological resilience of the lake.”

Wastewater treatment crucial

The nutrient enrichment problem cannot be solved unless appropriate levels of wastewater treatment are applied. But he said, “This is unlikely to be possible given the sheer volumes of effluent, the inadequate technology presently employed and the financial constraints of most South African local authority budgets.” 

The inability to deal effectively with the underlying causes moves the focus to one of having to “live with eutrophication”, Harding said. 

“If the water from affected reservoirs is required for human and animal consumption, the manner in which it is treated has to be augmented accordingly, of itself a significant cost factor. 

“If the reservoir is important for on-water recreation, for example rowing at Lake Roodeplaat, the swathes of hyacinth need to be removed or at least attenuated to a sufficient degree.”  

The available interventions become simply cosmetic. “By contrast, meaningful wastewater treatment is an absolute and unavoidable priority, especially in a water-scarce country.”

Allied to this is that the eutrophication issue of nutrients is a “proxy for everything else in wastewater”, including drugs, endocrine-disrupting chemicals, forever chemicals and microplastics, that are also not being dealt with and are ending up in the water resources.

Rapid hyacinth production

Water hyacinth in these reservoirs has no nutrient limitations which, coupled with the high ambient temperatures, long day lengths and the hyacinth’s very broad ecoclimatic adaptability, results in a biomass probably exceeding 200kg a hectare each day, he said. 

“Personally, I doubt that biocontrols can get out in front of such production rates,” he said, referring to the biological control of water hyacinth using the biocontrol agent, Megamelus scutellaris planthoppers.

“Even in South America, the natural home of both the plants and their natural enemies, the biocontrol organisms, plants in eutrophic waters reportedly can outgrow the insect damage, resulting in vast expanses of sick hyacinth but not eradicative control.  So, we may be just painting over the mould.”

He added that decomposing hyacinth is not an additional source of nutrients to Lake Hartbeespoort. “These plants grew using nutrients already in the lake, and when they decompose, a process which can leach as much as 59% of absorbed phosphorus in just a week, the nutrients are simply being returned back into the very pool they originated from. The scenario would only be valid if the plants had grown elsewhere and then been washed into a nutrient-poor waterbody.” 


In May, the department of water and sanitation officially appointed Magalies Water for a 36-month period, to implement a remediation plan focused on improving raw water quality in the Crocodile West catchment upstream, including Hartbeespoort Dam.

Its scope of work includes the removal of hyacinth in the Hartbeespoort Dam and along the catchment area; water quality monitoring and pollution tracking; implementation of the hyacinth and algae remediation; the implementation of effective and viable treatment technologies; and the development of potential business models based on circular economy and waste valorisation concepts.

Magalies Water spokesperson David Magae said, “The problem is already in the dam and the intervention should concurrently take place in the dam and upstream of the dam. Our plan caters for both. We will curb nutrients at the source yet fight the sequestrated nutrients that are already in the dam and buried in the sediments.” 

Harding said he is aware that Magalies Water had been appointed as the implementing agent for a second round of attempts to improve the conditions in Lake Hartbeespoort. 

“I, and others, are very concerned that a repeat of the eight years and R160 million of the Metsi a Me fiasco is again looming.

“I head up a specialist amicus group of reservoir limnologists and we requested, in March this year, to have sight of what is planned this time around. Thus far nothing has been shared with us, but I have been told that a contract for the manual removal of hyacinth is apparently underway.”  

Lakes cannot be all things to all people, Harding added. “What is important is that a desired state be agreed on and measures adopted to achieve the same. This will take much time, effort and considerable expenditure but, with the right supportive mindset, it is possible.”