Bulk water supplier Rand Water’s adaptive integrated management strategy is proving successful as it drives down the proliferation of aquatic invasive alien plants (IAPs), such as Pistia stratiotes, or water lettuce, and Pontederia crassipes, more commonly known as water hyacinth, in the Vaal River.

The strategy has led to a significant 190.44% decrease in coverage of the Vaal River Barrage Reservoir (VRBR) from peak infestation of 414 ha, or 31.84% coverage, in 2024, to just 0.46 ha, or 0.03% coverage, as at March 11.

“While conventional control methods are often unsustainable, costly and environmentally harmful, new technologies that include the implementation of an adaptive integrated management strategy have yielded positive results, particularly in the VRBR,” the utility says.

The approach, which Rand Water adopted after being contracted by the Department of Water and Sanitation (DWS), combines the use of curtains and chicanes, which are structures used for entrapping IAPs in isolation to avoid movement between sites on the watercourse, along with the physical removal of the plants through machinery like excavators, specialised watercraft and, where needed, manual labour, and the targeted use of approved herbicides such as Kilo Max and Seismic.

This is augmented by the release of biological control agents, including Neohydronomous affinis, Neochetina spp and Megamellus scutellaris.

As part of the adaptive strategy, areas of the VRBR have been identified and targeted for specific interventions, with the total area under management of the contract covering 1 300 ha of water surface of the VRBR.

The implementation of the strategy requires weekly monitoring of the entire system, early detection of new growth and robust quick action to address potential problem areas.

Since the start of the growing season from October 2025 to January 2026, Rand Water has removed 3 855 m3 of IAPs, introduced about 940 000 various species of biocontrol agents and administered herbicide on about 35 ha all through funding provided by the DWS over a three-year period.

The strategy has to be adaptive in nature to allow for flexibility in implementing control mechanisms – growth of IAPs can be sporadic and irregular over different growing seasons even in the same area – requiring adaptability in the management of the macrophytes.

Rand Water points out that it has been able to maintain less than 10 ha coverage, decreasing coverage from 18.95 ha in the growing season during February last year to 1.94 ha as at February 9 this year. It further highlights other vital aspects that led to its success, including robust public-private partnerships for the establishment of three dedicated local biological rearing stations by community members at their own cost, along with ongoing monitoring programmes in collaboration with government institutions such as the DWS and the departments of Forestry, Fisheries and Environment and Agriculture, Land Reform and Rural Development.

The partnerships enable the implementation of coordinated control, rehabilitation and maintenance interventions, while continuous monitoring programmes provide critical data to track infestation trends, assess the effectiveness of management actions and inform adaptive decision-making.

They are also supported by regular and ongoing community and stakeholder planning and feedback meetings, where project progress, feedback and plans are shared.

However, pollution of the VRBR still presents a significant challenge that is exacerbating the rampant growth of these plants.

“Added to this, seeds are viable for as long as 20 years, which implies that control and management of IAPs must be seen as a long-term project to prevent any future IAP blooms as seen in 2024,” Rand Water comments.