This thick green mat extends for as far as the eye can see, it's an unwanted, invasive South American aquatic plant species called Salvinia minima. Hidden beneath it is South Africa's Hartbeespoort Dam near Johannesburg, an important source of irrigation for nearby farms and a popular recreation site. This is also the site of the pilot project to tackle the Salvinia. The plant is steadily taking over freshwater bodies in the northern region of the country suffocating aquatic life, threatening eco-systems and creeping into neighbouring countries including Zimbabwe, Botswana and Mozambique.
Today the researchers and environment officials are aiming to fight back with little black beetles called weevils. They're being hurled in the dam so the weevils and their larvae can munch their way through the Salvinia damaging the tissue of the plant until it becomes waterlogged and sinks. After weevils effectively controlled Salvinia in Florida, scientists from South Africa and the United States worked together on a project to gather a starter population in southern Africa. The 1-millimetre-long (0.03 inches) insects were brought over 8,700 miles from Louisiana. Professor Julie Coetzee from the South African Institute for Aquatic Biodiversity is a specialist in tackling invasive species which threaten biodiversity. She explains why the weevils were chosen. “These insects were imported from Louisiana and the reason why we imported them from there is they're not indigenous to Louisiana, this is Louisiana in the United States, they've got this plant as a problematic invasive species and they've got a very good biocontrol program on this plant.”
According to scientists beetles released at an infested site are able to make themselves at home on the Salvinia without damaging the local ecosystem. Rearing stations are also being set up near various dams to grow the weevil population. “This plant and other invasives like it block out the sunlight, if they block out the sunlight into the water body, there can be no oxygen in that water body because the plants in that water body won't be creating oxygen through photosynthesis. If there's no oxygen, there's no fish, there's no crabs, there's no insects. And so you completely destroy or alter the aquatic ecosystem,” says Coetzee. South Africa’s already vulnerable freshwater systems face a significant threat from Salvinia and according to researchers it's had two major growth spurts in 2021 and 2022, surviving on the high nitrate contents in the water.
The plant initially surfaced on Hartbeespoort Dam in 2012. The site was already battling with a water hyacinth invasion. Max Moller the site's property owner and business operator says the plants have been an ongoing menace. He says: “I would imagine, because the quality of the water is so bad that it's pure fertilizer for these invasive species. And so what really happens is it seems to, yes it seems to have the effect of you know, about it seems to double its mass in about the 2 to 4 days, which is absolutely insane.” “The moment there is a flood okay, from here all that Salvina is pushed down the river into Hartebeespoort Dam. So it's just a never ending cycle,” says Moller who owns Mogi's Hiking Trail.
Sello Seitlholo the Deputy Minister of Water and Sanitation says the aim is to let use natural methods to control the Salvinia. “We obviously have to allow the biological process to take its course, because this is largely, you know, a process of attempting really through this particular process to deal and address the issue of the of the alien invasive species. So I'll take Prof. Julie's cue on that and say in about a year's time, we should be able to start seeing some form of difference." The bulk of the growth spurts have been recorded across Gauteng, compounding existing water issues including sporadic supply outages and limits on home water use.
The problems are exacerbated by increasing demand, deteriorating infrastructure, and poor municipal management. The government is considering imposing fines for polluting offenders. Seitlholo says: “The hyacinths in Harties (local name for Hartebeesport) is a very big challenge, and you would have seen in the earlier presentation that depending on the season, you've got more of it as it blooms and then there are certain seasons where you know, it's hardly there. And I think for us, it's going to be very important as a department to secure our water resource. But also what is going to be very important is for us to be able to really get into serious conversations with municipalities in the upper catchment who are largely responsible for the high nutrient load.”
The speedy growth of Salvinia in freshwater bodies across the country’s northern most provinces has put pressure on the government to act, particularly as researchers warn that neighbouring states face a potential threat of a Salvinia invasion. Coetzee says Salvinia is popping up on the confluence of the Crocodile and Limpopo River, meaning it would soon show up in other countries where water security is already unstable.