The weedy green mat of water hyacinth that once ruled Hartbeespoort Dam is retreating, now covering only 10% of the dam – down from an all-time peak of around 80%.
The infamous water hyacinth is being devoured by a tiny bug smaller than a grain of rice, introduced by scientists as a hyacinth ‘biological control’. This secret agent, called Megamelus scutellaris, is a 3mm planthopper native to South America which only feeds on water hyacinth.
Unlike humans, Megamelus scutellaris loves water hyacinth, and will die unless it feasts upon the plant. A team of scientists from Rhodes University therefore decided the bug was the perfect match for Hartbeespoort Dam, which has made a startling recovery since a 350,000-strong bug army was released into the dam last year.
This success is welcome news for anybody who has tried to plough their skiboat across the dam in recent years. At one stage the NSRI had to rescue tourists from a ferry trapped in the weed.
Sadly, the bugs have not solved the dam’s hypereutrophication problem. The water often looks like “pea soup” due to cyanobacteria (blue-green algae) fueled by upstream sewage pollution.