The Great Hyacinth heist

Post by Emma Oliver

Invasive water hyacinth has been an annual headache at Princess Vlei, lowering the quality of the habitat and clogging the water. Efforts to clear it with heavy machinery have been immensely destructive, costly, and ineffective. But a coordinated effort is bringing hope that this problem can finally be managed in a more effective and less destructive way.

 Tackling water hyacinth at Princess Vlei is an ongoing story of successes and failures as,  together with the CoCT, we have tried to come to grips with what is known as ‘the world's worst water weed’. Each year the situation gets worse as a carpet of the pretty but destructive water hyacinth spreads rapidly across the vlei.   The dense growth suffocates life beneath it, prevents access to the water, and disrupts the delicate balance in the vlei's aquatic eco-systems.
      In 2023 the City of Cape Town spent R9 million using heavy machinery to remove the water hyacinth. There was outcry over the amount spent, over the damage to the banks of the Vlei by the heavy machinery, and over the inadequacy of the operation to tackle the problem.   (See the post on the shoreline destruction). In 2024, no budget was allocated by the City to remove hyacinth, and the weed grew steadily. . There was a small die back in winter  but spring brought new growth, and now in summer it is  blossoming with its delicate lilac flowers and expanding rapidly.  The Southfield canal and Sassmeer outlets are completely clogged up. Hyacinth Islands blow across the Vlei,  and settle all around the shoreline, preventing access to the water. Dealing with it  is a daunting task that will take years of ongoing effort to manage.

      However, we have been given new hope that 2025 will be more constructive and productive. In June, the Princess Vlei Forum, via Nature Connect, received R60000 of a ‘noncompliance’ funding (funding given by a development project as penalty for flouting compliance requirements) which was to be spent on clearing invasive alien species. With this money we have bought a 15HP boat motor, a work boat, life jackets and waders, to be used by a boat team. We also raised funds for a boat team through Hans Hoheisen Charitable Trust  (managed by Nedbank Private Wealth). The boat team will be headed up by Sidney Jacobs from the Friends of Zeekoevlei and Rondevlei. Sidney’s team have much experience  in this field from work in Zeekoevlei. Funding raised by the Forum will give them 24 days working on the water.

    In August, the Zeekoevlei Catchment Forum was formed under the leadership of specialist fresh water ecologist, Dr Liz Day. Princess Vlei lies within the Zeekoe catchment. The Catchment Forum brings together people from many diverse fields – the CoCT, NGOs, Friends Groups, volunteers – to find ways to improve the health of the catchment. This collaboration has enabled the creation of the Princess Vlei water hyacinth clearing team. The team members include city officials from Recreation and Parks, which is responsible for the banks and land around the vlei; from Catchment, Storm water and River Management (CSRM) which is responsible for the water body and operates heavy machinery, booms in the water, and land teams for clearing the hyacinth once out of the water; from the Invasive Species Unit, under Bongani Zungu, which is breeding and introducing megamelus scutellaris, or water hyacinth planthoppers,  as biocontrol agents. Another key player is Jane Doherty, who is completing a PhD exploring whether biocontrol can be effective on water hyacinth in the Western Cape. The Forum is supplying the boat and boat team and other supplementary funding.
    The aim of biocontrol is to get the planthoppers in their thousands to eat the hyacinth, make holes in it, and cause it to sink and die.  Large numbers of megamelus bugs are crucial for an effective outcome. The ISU at Westlake is breeding megamelus, and the Forum is paying for an additional consignment of the water hyacinth planthoppers  to be couriered from the Waainek Rearing Facility at Rhodes University. The first consignment of 5000  bugs has already been released on hyacinth in the Southfield canal.   Several consignments will be needed. The biocontrol work is new territory for many on the team, and needs  to be carefully monitored. The success of the operation depends on good communication between the different players. For example, it is essential to ensure  that the CSRM heavy machinery contractors don’t remove the hyacinth where they bugs have been released.
     The challenge for the Forum will be to liaise, push, collaborate, demand and do what it takes to hold the water hyacinth team together and ensure that the CoCT departments, the CSRM, Recreation and Parks, the Invasive species unit all deliver.  However, persistence and determination is a quality we have developed over the years. Watch this space.
    Huge thanks to all involved, and to Nature Connect and Hans Hoheisen Charitable Trust managed by Nedbank Private Wealth for making this possible.