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. Of the 550 square kilometres of lagoon, 418 square kilometres are open to the tides of the Upper Adriatic, which is the highest in all of the Mediterranean.