Tides!

Tides are altered by the effects of the moon and sun which causes for the earth's water surface to change. These changes occur with the changing position of both the moon and the sun. Spring tides experience extreme high and extreme low tides with neap tides experiencing only moderate and average high and low tides. While in Venice Italy, many of the stores often have to deal with rising tides and worry about how the tides could one day "swallow up their stores." This is why the city of Venice builds concrete barriers to protect their precious property.