Coastal wetland communicating with the sea through gaps or inlets. As well as by exchanges with the sea, a lagoon is also characterised by a series of typical morphological and environmental elements: a system of main channels starting from the inlets and spreading through a network of smaller channels to penetrate as far as the innermost zones; a complex fabric of islands, mudflats and salt marshes; a succession of relatively deep areas (the average depth of the lagoon is 120 cm) and a "transitional zone" between the mainland and the lagoon consisting of lakes, marshes and reed beds (today in the Venice lagoon, this "transitional zone" has almost disappeared as the land has been reclaimed and occupied by agriculture, urban and industrial development, artificial canals and pumping stations). This variety and environmental and morphological complexity is a typical element of the lagoon ecosystem. The impoverishment and "simplification" of this complexity would signal the end of the lagoon itself. The disappearance of these elements implies not just the destruction of an immense environmental heritage, but also the loss of hydrodynamic, biological and productive functions essential to maintain the vitality and richness of one of the world's most productive habitats.