Hi Ryan
Much earlier than most people believe, when i was living up in JHB i would fish through out the year as there was not much else for me to do on weekends + company petrol. I have had some unbelieveable fishing in late August and September but the water she is very chilly !! I was fishing the deeper pools at Ben Joe and Vag Bietjie and had days of 20-30 fish and the place all to my self but water clarity and levels play a part! 15-20 Cumecs is ideal and as for the flys well the usual suspects do the job, hot spots, orange colour caddis , copper johns, olive purple black flash back nymphs small crab patterns and most of your caddis patterns if you are tying your own flys - weight them well or use split shot on your dropper and your point fly cause if your flys are not pouncing on the bottom you going to have far less takes! Dam i am so keen to get up there this season - yellow fish on fly is the berries i could almost say its some of the best fishing i have ever had! Let me know how it goes cause you might be seeing me up there pretty soon.
Cheers
TF