Rab,
I went to Lake Garda couple of years back, amazing place in general.
Fishing wise, I was on honeymoon with the missus, think i'd of been drowned if I had mentioned fishing
Where abouts are you staying? We stayed in Riva which is the big town at the most northern part of the lake, there are plenty of large fish swimming about really close in to the edge up around the ferry terminal there, (may or may not be carp) Lake Garda has all sorts in it.
have a read at this,,, you probably already have.. sounds like fishing on lake garda maybe worth giving a go
http://www.cemexangling.co.uk/forums/showthread.php?t=136945
sounds like some huge fish in it.
There is a smaller lake north of Lake Garda, Lago Di Tenno (check it on Google Maps) There was Villa to let there a few of the family had asked me to email about for a holiday and I asked them if they knew what fish was in Lago Di Tenno and they had not got a clue, and where not interested in finding out for me either lol.
Main tip Rab is take plenty of cash with you, one thing which has stuck in my mind about my visit to Lake Garda, we only went a week would love to go for 2, but we went on a tour guide type thing rather than just self catering along the south of the lake.
anyhow the thing which stuck lol, it cost us 8 Euro for 2 cans of coke in Sirmione. was pissing down the day we where there and thought screw this in outta the rain for 5 minutes, the Umberellas we had where leaking it was coming down so heavy. they definitely know how to charge. avoid venice.. well amazing place really nice to see.. but 2 extremely small meals (looked like a starter lol) and a coke each on the grand canal cost 50 euro.
have a great time Rab and if you do get fishing make sure you take some photo's of your catches would love to see what sort of fish and size comes out of it.
maybe contact where you are staying asap and see if they can give any advice on the fishing. the story we had been told by our tour operator is that the lake used to be fished by fishermen for years, who caught and sold the fish on. what happened was those fishermen had houses etc around the lake and because it became a more profitable business to open up hotels and guest houses they all done that instead so there is very rarely fishing boats out on the lake. I seen the odd person on a jetty fishing but nothing extreme similar to those on the link that mention people with a wee rod and float.