The dams in the Durbanville area (Sonstraal dam and Vygeboom dam) use to be surrounded with green grass and were previously home to families of the ordinary white ducks and geese. Over a period of a few years Egyptian gees started nesting in the area and soon overtook their white neighbours in number and appeared to push them out of the area. I remember watching the birds for some time and observing that the Egyptian gees appeared more hostile whereas the white ducks just looked clumsy and meek.
Today there are hundreds of Egyptian geese in the area and since they typically eat grass, leaves and seeds, it appears as though their sheer number overgrazing has rendered the once-green grassy areas barren and sandy. It's sad really - those two dams specifically use to be such beautiful places.