This little, brown warbler is almost impossible to differentiate from its European cousin; the eurasian reed warbler. In fact, in-hand examination is required to determine the differing wing structures, which separate these two species.
That said, one can be 99.9 % sure that if you see one of these reed warblers at Marievale Bird Sanctuary in winter, it is an African reed warbler (as its Eurasian counterpart is a rare summer migrant).
I first photographed this species in November 2010 at Marievale Bird Sanctuary. Nylsvlei Nature Reserve is another reliable spot for it.