Govt Deploys Weevils to Combat Invasive Aquatic Plants at Hartbeespoort Dam

The introduced species, Cyrtobagous salviniae, is a subaquatic herbivorous insect renowned for its ability to curtail the growth of the invasive salvinia plant.

In a groundbreaking effort to control invasive alien aquatic plants, Water and Sanitation Deputy Minister Sello Seitlholo, in collaboration with the Rhodes University Centre for Biological Control (CBC), has introduced weevil species at Hartbeespoort Dam in the North West. The release of these biological control agents marks a strategic intervention to mitigate the spread of Salvinia minima, a destructive floating aquatic weed commonly known as common salvinia.

The Role of the Salvinia Weevil

The introduced species, Cyrtobagous salviniae, is a subaquatic herbivorous insect renowned for its ability to curtail the growth of the invasive salvinia plant. Imported from Florida, USA, this weevil species has demonstrated significant success in managing similar infestations abroad. The initiative represents a crucial step in South Africa’s ongoing efforts to protect its freshwater ecosystems from invasive plant species.

Accompanied by Professor Julie Coetzee, Deputy Director of the CBC and Principal Scientist at the National Research Foundation’s South African Institute for Aquatic Biodiversity, Seitlholo officiated the weevil release at Mogi Adventures, near the Crocodile River.

Escalating Environmental Threats

The presence of Salvinia minima at Hartbeespoort Dam was first documented in 2011, and since then, its rapid proliferation has impacted water systems in North West, Gauteng, and as far as the Limpopo River, which borders Botswana. This expansion poses a severe threat to South Africa’s freshwater ecosystems, affecting biodiversity, water quality, and economic activities reliant on water bodies.

Expected Impact and Monitoring Efforts

Professor Coetzee emphasized that the weevil population is expected to multiply swiftly, with tangible effects on the common salvinia plant observable within a year. The CBC, working alongside local communities, will facilitate weevil rearing and strategic releases at multiple affected sites across the country.

“This biological control programme will be closely monitored to assess the weevil’s progress and effectiveness in reducing common salvinia. Importantly, these weevils exclusively target the salvinia minima plant and do not pose risks to other aquatic vegetation, crops, or ornamental plants,” Coetzee assured.

Addressing Pollution and Water Management Challenges

Deputy Minister Seitlholo highlighted the necessity of integrating biological control measures with broader environmental management strategies. A major contributing factor to the proliferation of invasive aquatic plants is nutrient pollution caused by substandard wastewater treatment. Seitlholo stressed the need for collaboration with municipalities to improve wastewater management and prevent excessive nutrient discharge into rivers and dams.

“What is also important is for us to have serious discussions with municipalities in the upper catchment areas. The inadequate treatment of wastewater leads to high nutrient levels in the water, which in turn fuels the spread of invasive aquatic plants, degrading the ecosystem, affecting recreational activities, and hampering the local economy,” Seitlholo said.

Complementary Remediation Strategies Alongside the introduction of weevils, the government is implementing additional remediation initiatives at Hartbeespoort Dam, spearheaded by Magalies Water. These measures include the mechanical removal of water hyacinth and a pilot project utilizing nanobubble technology, which enhances dissolved oxygen levels in the water to accelerate the breakdown of organic matter.

Since water quality remains significantly affected by untreated wastewater and sewage discharges from municipalities such as Tshwane, Johannesburg, and Ekurhuleni, Seitlholo urged municipalities to actively engage in remediation programs to rehabilitate water resources.

Strengthening Legislative Measures To reinforce accountability, the Department of Water and Sanitation is pursuing amendments to Section 19 of the National Water Act (NWA). These amendments, currently under review by the State Law Advisor, aim to hold executive mayors and municipal managers directly accountable for municipal violations related to water pollution.

“These legislative measures are critical in addressing water pollution at its root cause and ensuring long-term protection of our water resources,” Seitlholo affirmed.

Conclusion The deployment of the salvinia weevil represents a progressive step in combatting invasive aquatic species at Hartbeespoort Dam. While biological control offers a sustainable solution, it must be complemented by robust pollution control strategies and legislative reinforcements. The success of this initiative will not only restore ecological balance but also protect South Africa’s valuable water resources for future generations.