This was highlighted in the Status Report on Biological Invasions in South Africa, which was released by the South African National Biodiversity Institute (Sanbi).
Sanbi director for Invasive Monitoring and Reporting Sebataolo Rahlao said invasive alien plants reduced surface water runoff from 1 500 to 2 500 million cubic metres a year. Primary catchments areas most affected were in the Western and Eastern Cape and in KwaZulu-Natal.
Rahlao said: “Because of their deep-root system, they take off water that would have been available for our access; they are essentially extracting from our water. We should be worried about it.”
He said the issue of invasive species was a historical one and not one that could be resolved overnight.
“Now they are expanding on their own and you find a lot of trees and species growing along areas with water. They are expanding because the conditions are suitable and they are expanding each year.”
Rahlao said much had been done over the years to address the issue of alien species, but there was a long way to go.
The report is the first of its kind and has been called a milestone for the country. It will be followed by repeat assessments every three years.
“Next we will look at what other impacts these invasive species have, such as health, livelihood and economic impacts”
Meanwhile, dam levels in the province dropped by 0.6% over the past week to 74.1% capacity. Cape Town’s average water consumption decreased by 34 million litres a day to 559 million litres a day the past week.
MEC for local government, environmental affairs and development planning Anton Bredell said: “We are headed for a difficult summer period, with high temperatures and increases in demand.
"We need to continue to manage our available resources optimally. We have no certainty about what next winter’s rainfall will look like.”