Rand Water to Tackle Invasive Water Plants on Vaal River Barrage Reservoir

An explosive growth of these plants occurred in early 2024, driven by a combination of nutrient-rich effluent spills, high summer temperatures, and reduced water flow.

Rand Water has announced its collaboration with the Centre for Biological Control (CBC) to combat the spread of invasive water plants on the Vaal River Barrage reservoir. The effort focuses on Pontederia crassipes (water hyacinth) and Pistia stratiotes (water lettuce), both highly invasive species threatening local ecosystems.

An explosive growth of these plants occurred in early 2024, driven by a combination of nutrient-rich effluent spills, high summer temperatures, and reduced water flow. At its peak, the infestation covered approximately 397 hectares of the 940 hectares under monitoring.

Thanks to local community efforts, pro-bono support from Rhodes University's CBC, and physical removal efforts by Rand Water, the infestation has been significantly reduced to less than 1 hectare as of early spring 2024.

A Comprehensive Integrated Approach

Rand Water has adopted an integrated control strategy involving:

Physical removal of plants during dormant winter months.

Chemical spraying, used only when other methods are insufficient.

Curtaining techniques in water courses.

Biocontrol agents, which are environmentally sustainable and host-specific.

To ensure long-term management, Rand Water has appointed the CBC, South Africa's leading institution in biological control, as the sole service provider for the upcoming season. The CBC team, led by Professor Julie Coetzee, Dr. Kelby English, and Professor Martin Hill, will oversee biocontrol implementation, training, and monitoring.

Permits and Biocontrol Agents

The Department of Forestry, Fisheries, and Environment has granted Rand Water four permits to rear biocontrol agents. These will operate at Rand Water’s nursery and three community-run sites, funded by local contributions.

The biocontrol agents include:

Neohydronomus affinis (water lettuce weevil).

Megamelus scutellaris (water hyacinth hopper).

Neochetina bruchi (water hyacinth weevil).

Neochetina eichhorniae (water hyacinth weevil).

These agents are rigorously tested to ensure they exclusively target water hyacinth and water lettuce, completing their life cycles on these host plants without affecting native flora.

Long-Term Goals and Community Involvement

Rand Water emphasizes that addressing the seed bank already present in the water will require sustained efforts. The agency aims to rely heavily on biocontrol while integrating other methods when necessary.

Community involvement has been a cornerstone of this initiative. Locally funded rearing sites not only enhance control efforts but also empower communities with the tools and knowledge to combat invasive species.

A Step Towards Restoring the Ecosystem

This project underscores Rand Water’s commitment to preserving aquatic ecosystems and supporting biodiversity. The integrated approach, combined with expert guidance from the CBC, ensures a sustainable and effective solution to the challenge posed by invasive aquatic plants.

The collaboration offers hope for a healthier Vaal River Barrage reservoir and a model for tackling similar environmental challenges nationwide.