No, at the end is not so difficult if you accept the fact that Venice is a totally different town so you cannot easily carry in and out every kind of stuff, and obviously then inside the town you can only go around walking or with a boat. For me is all this is a normal thing, I can understand that living this way is somewhat crazy for the rest of the world.
So it depends from where your friends live. And in any case some parts of the lagoon are still untouched.
South lagoon should be more (even too much) deep, but obvioulsy the big 70 cm fin is not the best choice, at least on has to carry a seaweed inside a backpack.