There are a few smaller of the large dams near to Durban that are popular with float-tubers/kick-boaters. You can try Hazelmere, Mnini, Shongweni or Nagle Dams. Otherwise there are many places a bit further inland with small farm dams - also Tuckers down the South Coast.
Speak to Cranky on this forum - he's in a group of kick-boaters that regularly go on fishing expeditions together. (He'll probably reply in this thread anyway)