I'm only 40 miles from Kelowna , Most of the flyfishing around there is for stillwater trout in In the higher lakes in August . I suggest you drop in to Troutwater fishing flyshop in Kelowna , they will have the best advice . It may be another very dry year this year , with the possiblility of a forest closure . We narrowly avoided one last year with a late August rain . Upper lakes can be spectacular with some large rainbow . I regularly used to fish Okanagan lake for large Rainbow in the 10 to 20 pound range . I average about 10 fish over 10 pounds each year . All were caught trolling with very light gear and small hooks no weight so I believe flies should work there too . You need a large boat for Okanagan lake because of the high winds which can be dangerous to small boats . It is a very tricky lake to fish , very deep , 800ft or so average depth is 300 or more ft . I'm going to try bucktailing it this year , I'd like to get a 10lb on a fly . I'd like to say I could help you with the whereto , howto , and whatwith for flyfishing but I'm new at it myself . I just started late last fall . I do know that we use the worlds smallest chronimids around here in August . Down to size #24 . There are many smaller lakes with good access and many have lodges or crude camping facilities within a couple hours drive of Kelowna , but almost no good rivers or streams. About a 2 1/2 hour drive will take you north to the South Tompson river area and Salmon country . I don't fish that area and dont know what time of year is best , but it has some very good runs . There again check with the locals . Phil Rowleys fly patterns for stillwaters is recommended reading if you can find a copy.