I live in Buenos Aires, but have never dived in Argentina. For sure you will not be able to dive near Buenos Aires city since we only have a river here. I know that the best places to dive are in "Peninsula Valdez" where the water is cold but where you can dive with whales, the only thing is that is rahter far from Bs As and you will need to take a plane. Other suggestions, enter yahoo.com.ar and type "buceo" there you can choose some of the scuba shops in Bs As.