Hi mate, one of the beaties of fly fishing is it's versatility. You can fish anywhere for near on any species, certainly any fresh water species can be taken on the fly; so yes, fishing a dam is no problem. Also with regard to casting intruction many trout reservoirs have instructors on site, I don't know the set up where you are, but I guess that will be the case everywhere(?). Welcome to the wonderful world of fly fishing, you won't regret it. Tight lines.