There are lots of people swimming in Lake Garda, especially this time of the year. I am not too sure if you could catch fish there. But It will be interesting to know about fishing in Lake Garda. Maybe a little bit further from the shore if you have a boat?
I believe you can catch perch, pike and even trout there. But it might not be the best time of year. At the moment it's very touristic and hot. Finding the fish could be a problem, it's a big lake. You'd probably have your best chances fishing in deeper water. Best if you can organise a boat (with fish finder if possible) Or perhaps try night fishing.
Yes lake garda is hectic and hot this time of the year. I have fished the southern end of the lake for carp( very few tourist where the lake empties into the river) I want to try pike fishing this fall but many of the local fishermen are tight lipped when it comes to good fishing spots. During the spawn mid July thru end of August lake sardines can be caught by the hundreds if your at the right place both on shore and from a boat. Boat fishing for pike is the way to go but it's such a big lake location is everything. I will keep you updated.