Hyacinth surface cover at Hartbeespoort Dam is currently down to an estimated 22%, and the leaves are stressed and turning brown, mainly due to biological control causing a slowdown in growth. The hyacinth mat is currently sinking.

According to Hartbeespoort scientist and consultant for the former successful Metsi-a-me Hartbeespoort remediation programme, Frikkie Botha, the invader plant salvinia minima may soon become visible since the nutrient level in the water is hypertrophic.

“It is expected that decaying water hyacinths may sink and become dead organic material at all levels of the dam on the sediment. This can lead to carbon dioxide in the shallow part and methane in the anoxic part of the dam. Due to the extended open areas of the dam, the threat of oxygen deficiency for large fish (e.g carp) is much less as oxygen can enter the water body on the turbulent surface.”

In January, it was predicted that due to a two-month delay in water hyacinth germination in late 2022, the mat should sink by the end of April as a result of biocontrol and no herbicide intervention.