"Element opposes element". This is how Bernardo Trevisan described the lagoon in 1718, as an environment subject to the actions of different forces, natural or man-made, which oppose one another.
The lagoon is in fact a wetland coastal area in a continual state of instability which communicates with the sea through openings, or inlets, in such a way that the movement of water inside it is governed by the tide. In this way, lagoon morphology depends on the relationship between the amounts of solid material brought by the sea or the rivers and the erosive forces of waves and seas. Communication between the lagoon and the sea guarantees, among other things, the survival of the lagoon and its unique brackish water environment. The physical shape of the lagoon is modified and formed through the daily entrance and exit of the sea through the lagoon inlets. The sea can also be considered one of the main risk factors involved in the evolution of the lagoon basin, especially if the erosive actions of wave motion and coastal currents predominate over the build up of sediment accumulation. About 78% of the lagoon surface is covered by vast expanses of water which are cut by a dense network of channels of varying depth. The sea and the lagoon are connected through the three inlets of Lido, Malamocco and Chioggia.
The land system of the lagoon territory is made up of all of dry land, natural or artificial (coastal strips, reclaimed areas, islands and banks), and represents about 8% of the overall surface area of the lagoon. The remaining 92% is made up of the water system which includes canals (11.9%) and shallows, mud flats and salt marshes (80.1%). Mud flats are areas with no vegetation which are normally underwater, emerging only during particular tidal conditions (low tides during spring tide cycles); they are soft land areas. Salt marshes are important because of their role in regulating lagoon hydrodynamics. They are consistent ground areas which are almost always above water and are only sometimes submerged. They enhance water exchange, lessen the action of wave motion and provide a home for both a wide variety of vegetation (typical of brackish water areas) and for a wide variety of bird life.