City checks plant-invader threat to Zeekoevlei

Water hyacinth in the Big Lotus River was threatening the river system and Zeekoevlei.

The City has cleared pockets of invasive water hyacinth in the Big Lotus River, stopping them from choking the river system and invading Zeekoevlei.

The aggressive plant invader posed a “massive threat” to the river system,“ says Marian Nieuwoudt, mayoral committee member for spatial planning and environment.

“If left untreated, its population numbers would have soared and eventually choked the river system, with the risk of invasion of the 256-hectare open- water recreational water body at Zeekoevlei which is part of the False Bay Nature Reserve,” she said.

“Water catchments that are connected to the rivers where the plant is present, as is the case at Zeekoevlei, are under constant threat as the water hyacinth has the potential to cover 100% of the waterways and water bodies.”

False Bay Nature Reserve staff discovered the hyacinth at an early stage and used herbicide on it.

“Our team at the reserve had to act fast,” Ms Nieuwoudt said. “This was the quickest method to curb the reproduction of the plants and to minimise the threat of invasion.”

The treatment had killed the water hyacinth and there would be follow-ups over the next two weeks until no new plants were found.

According to Sidney Jacobs, chairman of the Friends of Zeekoevlei and Rondevlei (FOZR), water hyacinth is a herbaceous, free-floating aquatic plant with erect aerial leaves, lilac flowers and submerged roots.

“The ability to float means that it can be hidden under other plants while it grows at a fast rate, and then gets dispersed across the water body by the wind very effectively,” he said.

The plant is not poisonous, but it can take over an entire water body very quickly.

“The conditions created by water hyacinth encourage the vectors of several human diseases, including the intermediate snail hosts of bilharzia (schistosomiasis) and most mosquito vectors, including those responsible for the transmission of malaria, encephalitis and filariasis. Filariasis is a parasitic disease caused by an infection with roundworms of the filarioidea type. These are spread by blood-feeding insects such as black flies and mosquitoes.”

Water hyacinth also interferes with water treatment, irrigation, and water supply. “It can smother aquatic life by deoxygenating the water, and it reduces nutrients for young fish in sheltered bays,” Mr Jacobs said.

“It is also a massive threat to our endangered western leopard toad population that has re-established its breed in Zeekoevlei, thanks to the efforts by so many to create an optimum habitat for them to breed.”

Ms Nieuwoudt thanked FOZR members and shoreline residents for alerting the City to water hyacinth or removing the plant themselves.

Mr Jacobs said a “huge team effort” involving staff from the City and the reserve had stopped the hyacinth in the Big Lotus River, the main feeder into Zeekoevlei.

Two FBNR staff had been out on a boat daily checking the vlei and its inlets, Mr Jacobs said.

“They are often seen offloading hyacinth that had been uncovered under the other reeds.”

Ms Nieuwoudt said that prior to 2009 most of the Zeekoevlei catchment had been infested.

“At the time, the City succeeded in eradicating the plant from the system, and we enjoyed eight years of a hyacinth-free catchment. Unfortunately, water hyacinth was rediscovered in 2017.

“Efforts to eradicate this very invasive species from our nutrient rich rivers and vleis remain a priority.”