Cape Town - A concerning bloom of water hyacinth, the world’s most invasive and harmful aquatic weed, has been observed within the Zeekoevlei wetland over the past two weeks.
The sightings have prompted concern from the City and stakeholders of the vlei due to the detrimental impact this species could have on the waterway’s ecosystem.
Deputy mayor and spatial planning and environment Mayco member Eddie Andrews said: “While under control for many years, the recent bloom of water hyacinth at Zeekoevlei wetland is of concern.
“Water hyacinth, if left uncontrolled, can quickly cover a water body. This not only hampers any recreational use but also blocks out sunlight from the water column. As a result, all plants on the vlei bottom die, affecting the entire ecosystem.”
The nature reserve staff continuously monitor the water hyacinth and remove it from the Zeekoevlei whenever it is found. Andrews said a large patch of water hyacinth was found two weeks ago and plans to tackle it are at an advanced stage.
Friends of Zeekoevlei and Rondevlei (FOZR) vice-chairperson Tom Schwerdtfeger said: “We have experienced small patches of water hyacinth in Zeekoevlei for the last six months, and have managed to deal with those effectively.
“Unfortunately, with the ingress of phosphates from Phillipi farmlands and high levels of ecoli currently in Zeekoevlei, the ‘perfect storm’ scenario exists for hyacinth to thrive.”
The City’s environmental management staff at the reserve work closely with FOZR and are involved in the current removal programme. The teams anticipate that it will take about three months to get on top of the problem, with continuous monitoring for at least another three months thereafter.
FOZR has already removed some of the growth and a massive clearing operation was planned for this Saturday with the City and community partners to help remove the invasive species before it spreads into the main body of the vlei.
Should the hyacinth spread to the main section of the vlei, there would be a number of immediate challenges, said Schwerdtfeger.
Sailing and rowing will not be possible, and if the water hyacinth covers the surface of the vlei, it will stop sunlight from entering the water, resulting in the water temperature dropping and the underwater ecosystem dying.
Alex Lansdowne, deputy chairperson of the mayoral advisory committee on water quality in wetlands and waterways, explained that water hyacinth was the most invasive species in the world and particularly problematic in Cape Town in the Zeekoe Catchment, which includes Princess Vlei, Rondevlei and Zeekoevlei.
“City officials conduct seasonal manual removal at these waterbodies to control and manage the species. Our invasive species unit breeds and releases bio-control on a regular basis to stunt their growth. Our long-term goal is to cut off nutrients and pollution into these waterbodies to inhibit this invasive species from degrading them,” Lansdowne said.
Lansdowne said it was important that water hyacinth strategies in the short term and long term align to avoid a situation in Cape Town like that at Hartbeespoort Dam, where the water hyacinth has rendered the water body unusable
Schwerdtfeger said: “We urge all residents and recreational users of Zeekoevlei to get involved and play their part in ensuring that we can contain the challenge.”
kristin.engel@inl.co.za