Acqua Alta, Venice
In winter (oct-jan) it's possible to see this phaenomenon:you just have to buy some plastic boots in shoeshops.S.Marco place is one of the lower parts of Venice so, when the High water comes,it's really high and often your boots are not sufficient.In this picture you can see a part of S.Marco place and you see that my boots weren't tall enough!I think it's fun for a tourist,it's so for me too!!
Lorenzoh and me.
Although when we were in Venice the weather was very pleasant, I understand it can flood due to high tides. I don't think this stops the tourists but obviously it would be better to be prepared for it in case you arrived and it was flooded.
Be careful by the places on the shore of the sea!
The stairs are slippery and the water is malodorous and dirty.
Go not too near; it is dangerous to fall into the water!
If you are there at high tide you will find lots of the streets and piazze flooded. There are lots of shops that sell boots to wear just for this purpose.
St. Marks square has a tendency to become flooded, usually between January and March. Be forewarned and prepare yourself. I would bring some appropriate footwear.