With reference to your news report on the Kariba weed "problem". Years ago I got a distinction for a botany honours seminar I presented in which I stated that it was not the plant that was the problem, but the environment. Southern Cape fresh waters in their natural state are nutrient-poor. If there is a "bloom" of "weed" it means that the water is enriched, i.e. "polluted".
Spraying the plant does absolutely nothing to solve the problem as the dead plants sink to the bottom and that just adds to the rotting organic mass and nutrient "overload" in the dam.
In more technically advanced societies plants like salvinia (Kariba weed) or eichornia (water hyacinth) are, in fact, often used in water treatment works - in specially designed water runways - to help purify the water.
It is then harvested and composted or used as pig food thus "reclaiming" the valuable phosphates and nitrates that it has absorbed.
Destroying the Kariba weed could eventually even lead to toxic algal blooms, that formerly plagued the Hartebeespoort dam near Pretoria.
In summary, by destroying the Kariba weed you are just "shooting the messenger".