As South Africa’s urban rivers choke on plastic and wastewater, downstream farmers bear the brunt. Dr Kyle van Heyde from the ARC’s natural resources and engineering division explains how polluted rivers and degraded soils threaten rural livelihoods.
Water pollution in South Africa’s urban rivers and dams is widely recognised as a growing environmental and public health concern. However, far less attention is given to what happens downstream, where farms and smallholdings may depend on these same water sources for irrigation and livestock.
Rivers flowing out of urban centres can act as conduits of pollution, carrying contaminants into peri-urban and rural landscapes, shifting much of the burden onto communities that rely directly on these systems for their livelihoods.
South Africa’s constitution guarantees the right to an environment that is not harmful to health or well-being. In reality, however, communities along polluted rivers are often disproportionately affected, facing declining water quality, reduced agricultural productivity and increased health risks.
Pollution doesn’t travel alone
Urban water pollution is not a singular issue, but a combination of stressors moving through hydrologically interconnected systems. Wastewater discharges, stormwater runoff, industrial effluents, legacy mining, and poor waste management all contribute to declining water quality.
One overlooked concern is how these pollutants interact. Plastic debris is a useful example. Because plastics are buoyant and durable, they can travel long distances through rivers and dams. Once in the water, they become coated with biofilms that may harbour harmful bacteria and pathogens. This means pollution is not only transported downstream but can also change in character along the way (Figure 1).
Rainfall can intensify this process. Although rain is often assumed to dilute pollution, urban runoff can wash contaminants from roads, soils and infrastructure into waterways. Pollutants settled in riverbeds or along riverbanks can also be remobilised, sending pulses of nutrients, pathogens and chemicals into downstream agricultural areas.
Impacts on crops and soil
For farmers, water quality directly affects productivity. High nutrient levels are common in polluted systems receiving wastewater inputs. While nutrients are essential for plant growth, excessive concentrations can disrupt soil chemistry, affect crop health, and lead to imbalances that reduce yields or yield quality over time.
In eutrophic systems such as Hartbeespoort Dam, irrigation water can carry high nutrient loads and organic material that contribute to soil degradation and longer-term management challenges. Elevated ammonia can become toxic to crops, while high salinity may burn plant tissues and disrupt the soil microbial communities that support fertility, increasing input costs and reducing long-term productivity.
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Risks to livestock
Livestock are also vulnerable to poor water quality. Many smallholder, communal and commercial farmers rely on rivers and dams as primary water sources for animals. When these sources are contaminated, livestock may be exposed to pathogens and pollutants that cause illness, reduce productivity or contribute to disease outbreaks.
For smallholder farmers, the loss of even one animal can have serious economic and social consequences, affecting food security and household income.
Building resilience in agricultural landscapes
While addressing pollution at its source remains critical, there is also scope to build resilience within affected agricultural landscapes. Wetlands and riparian zones filter pollutants, trap sediments and improve water quality. When protected or restored, they can act as buffers that reduce the impacts of upstream pollution.
Farmers and landowners can also help reduce visible pollution before it moves further downstream. Where safe and appropriate, litter traps, floating capture nets, debris booms and regular clean-up points can intercept plastic waste in farm channels, drainage lines and small streams.
These systems must be carefully placed and maintained so they do not worsen flooding, block natural flow or release trapped material during high-flow events.
Applied research and advisory support are also important. Through ARC-Natural Resources and Engineering, water quality-related research, assessment and advisory services can support farmers with practical decision-making, including identifying water quality risks, safer abstraction points and periods when water use may carry greater risk.
Looking ahead
Water quality is not only an environmental issue, but an agricultural, economic and social one. Improving South Africa’s rivers will require coordinated action across sectors, including better urban infrastructure management, stronger wastewater regulation, and investment in restoration and remediation.
For farmers, practical steps such as protecting riparian buffers and wetlands, intercepting plastic debris where appropriate, and making informed decisions about when and where to abstract water can reduce exposure to polluted water.
Ultimately, clean and reliable water is about more than ecosystem protection. It is about safeguarding agricultural productivity, rural livelihoods and the resilience of communities that depend on rivers and dams. For more information, visit the ARC-Natural Resources and Engineering Services page on the ARC website.
- The views and opinions expressed in this article are those of the author and do not necessarily reflect the views or positions of Food For Mzansi.
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