The Venetian region is probably one of the best regions in Italy for flyfishing.
The Piave river plays an important role for fishing marble trout and hybrid. In some pools there are nice grayling too.
In Belluno, there is the possibility to catch with a dry fly trouts above 16 inches, and with a little luck and skill, even some in the 20 ” range are not impossible. In Cortina d’Ampezzo the Boite river contains a good number of brown trout.
Stillwater flyfishing is done in the Spring and Summer on pristine and very scenic alpine lakes.
The nearby region Alto Adige has a lot of good waters too!