It is only in recent decades that the value of wetlands has been properly understood. Wetlands provide a habitat for a diverse range of plants and animals. More importantly they play a valuable role in filtering the water that flows through them. In the case of the Westlake Wetlands this means cleaner water for the main body of the Zandvlei Estuary.
Westlake Wetlands are an important part of Zandvlei as they receive their water (prior to the water reaching Zandvlei) from two rivers that been seriously impacted by city decisions and invasive water plants over the years. Since 2002, a group of local volunteers regularly review, research and maintain the water body in this section of the Westlake Wetlands in partnership with the local authorities.
Westlake Wetlands Project has led the way in clearing the water hyacinth from these wetlands, with spin-off benefits for the rest of the city’s rivers and water systems.
Removing invasive plants promotes the biodiversity of all living species including insects, reptiles, amphibians, mammals and birds. The last remaining natural vegetation areas within the City are under extreme pressure from human development. Our natural areas need linking corridors of local indigenous vegetation to remain viable for the free movement of all creatures and the distribution of wind dispersed seed.
Invasive vegetation often dominates and suppresses indigenous plants. They grow quickly, using large amounts of water and also create a shade canopy preventing sunlight from reaching the ground, where the low growing, bulbs and seedlings struggle to thrive in low sunlight.
Fish cannot survive in water that has a ‘carpet’ of weeds covering it because it reduces sunlight and the oxygen in the water.
“When the fish go, the birds that live on the fish go as well. It has a dramatic impact on the ecosystem – that’s why we must keep the water open and flowing,” – John Fowkes
In addition to manual clearing of the invasive hyacinth, the introduction of the floating boom mechanism holds the weeds back from spreading into open water. These are made of 2 litre plastic cold drink bottles placed in a netting sleeve.
The floating booms act as a security barrier against potential future infestation and help contain any areas still harbouring hyacinth. Over time the bottles deteriorate, mainly due to temperature changes causing expansion and contraction. These bottles are then replaced with new stock and the old bottles are bagged and sent for recycling.
The effect of this work can be seen in an increase in fish activity. This in turn has led to an increasing number of kingfishers, herons and cormorants that, together with a number of people, come to fish in the cleared waters. The endangered Leopard Toad population also appears to have spread into some of the cleared areas.
So through innovative thinking, community action and collaboration with a range of partners, litter has been turned into booms that help combat an environmental threat. One could say that this initiative is booming success!
Invading water hyacinth
Clearing of aggressively invading water hyacinth (Eichhornia crassipes) from the Westlake River confluence with Zandvlei was among the Trust’s earlier projects. Floating booms (made of strings of 2-litre plastic cooldrink bottles placed in netting sleeves) were installed across the two rivers entering the Westlake wetland in order to prevent hyacinth from entering the main vlei water body.
Also, regular clearings of the weed “carpet” was organised. These efforts were underwritten at the time by PenBev cooldrink supply company and driven by early Trust champions John Fowkes and Gavin Lawson.
More recently, the City’s bio-diversity department has undertaken natural biological control measures, introducing a species of wee, plant target-specific weevil (Neochetina eichhorniae) to reduce and – hopefully – remove this aggressive invader or, at the very least, keep it down to manageable seasonal levels.
The weevils cannot cope with our winters, the weed being of tropical origin, so have to re-introduced early each summer if they are to be effective. Funds which the Trust holds for the clearing of hyacinth are currently dormant, for possible future later use or in other projects.
Our efforts to maintain the tranquil Westlake Pond are only possible with your support. Help us continue this vital work.