Crystabel Ukwuegbu
A vast green layer stretches endlessly across the surface of South Africa’s Hartbeespoort Dam, concealing the freshwater body beneath. This dense vegetation is Salvinia minima, an invasive aquatic plant from South America that is rapidly spreading across northern South Africa. The plant poses a severe threat to local ecosystems by suffocating aquatic life and is now expanding into neighboring countries such as Zimbabwe, Botswana, and Mozambique.
To tackle this growing environmental challenge, scientists and environmental officials have turned to a natural solution—tiny black beetles known as weevils. These insects are being released into the dam, where they and their larvae will feed on the Salvinia, damaging its tissue until it absorbs water and sinks. This method has already proven effective in Florida, leading to a collaborative effort between researchers from South Africa and the United States to introduce the weevils to southern Africa.
Professor Julie Coetzee from the South African Institute for Aquatic Biodiversity, a specialist in invasive species control, explains the reasoning behind this approach. “These weevils were sourced from Louisiana in the United States, where they have successfully been used to manage Salvinia, which is also an invasive species there. Their introduction here follows a well-established biocontrol strategy.”
Experts emphasize that these beetles can adapt to affected sites without harming native species. To ensure sustained control, rearing stations are being established near several dams to cultivate more weevils for release. Coetzee warns that Salvinia and similar invasive plants block sunlight from reaching the water, leading to a depletion of oxygen levels. “Without oxygen, aquatic life—such as fish, crabs, and insects—cannot survive, which ultimately disrupts the entire ecosystem,” she explains. South Africa’s fragile freshwater resources have already been affected by Salvinia, which has experienced two major growth surges in 2021 and 2022, thriving in nutrient-rich water caused by high nitrate levels.
The problem began in 2012 when Salvinia was first detected in Hartbeespoort Dam, an area already struggling with an invasion of water hyacinth. According to Max Moller, a local property owner and business operator, poor water quality has allowed these invasive plants to flourish. “The water is so nutrient-rich that it acts like fertilizer for these plants. Their mass seems to double within just two to four days, which is alarming,” he says. The infestation is further exacerbated by floods, which push the Salvinia downstream into the dam, creating an ongoing cycle of reinfestation.
South Africa’s Deputy Minister of Water and Sanitation, Sello Seitlholo, emphasizes the government’s commitment to using natural control methods. “We must let the natural process take its course.” Based on previous studies, we expect to see noticeable progress within a year,” he states. The Salvinia crisis has been particularly severe in Gauteng, worsening existing water challenges such as inconsistent supply and increasing restrictions on household water usage.
Other factors, including rising demand, aging infrastructure, and poor municipal oversight, have intensified the issue. In response, the government is considering imposing fines on polluters responsible for high nutrient loads in water bodies. Seitlholo highlights that managing invasive species like Salvinia and water hyacinth requires cooperation with municipalities in affected regions. “Hartbeespoort Dam’s hyacinth problem fluctuates with the seasons, but securing our water resources must be a priority,” he notes.
With Salvinia rapidly spreading in South Africa’s northernmost provinces, researchers warn that neighboring countries could soon face similar environmental risks. Coetzee points out that the plant has already appeared at the junction of the Crocodile and Limpopo Rivers, signaling its potential spread into regions where water security is already fragile. As authorities race to contain the infestation, biological control methods like weevil deployment may provide a sustainable long-term solution.
