The lagoon system of FVG extends between the mouth of the Isonzo and that of the Tagliamento. Compared to its “big sister”, the Venetian lagoon, it has been transformed far less by man with long stretches of barrier island in a natural state and river mouths in the lagoon surrounded by extensive reed beds. The “valli” fish pools are well represented in the lagoon of Grado while the lagoon of Marano is more open, less salty and deeper, with large areas that are never or rarely left above water at low tide. These transitional environments are typically dynamic with two fundamental trends: in one, sedimentation and building up of terrain prevails while in the other, there is erosion and transformation into a shallow sea. Man, especially in the last century, has worked to fix this changeable environment delimiting the area with embankments on the landward side to reclaim the lagoon, establishing outlets with breakwaters, building coastal barriers and reducing the number of outlets, thereby creating tideless fish pools. Today the lagoon is smaller and deeper than in the past and the natural trends or those induced by human activities directly or indirectly, have led to the gradual disappearance of the emerging areas with the erosion  of the coast and tidal flats. Clearly not all the sites show the same trends and in large areas of the coast silting prevails. Similar trends have occurred in Venice too, where they have been partly countered by building artificial tidal flats. The lagoon of Marano, less transformed than that of Grado, is now affected by strong and rapid evolutionary trends that have raised fears for areas near the mouth under the influence of the sea. From the ornithological point of view, this is one of the most important areas in Italy and the Mediterranean. If we consider the entire system of estuaries and lagoons of the northern Adriatic of which the area in question forms the north-eastern portion, this is the largest Italian wetland. Over 300 bird species have been observed here, of which about 110 nest, not all regularly. These high numbers increase if we consider the lowland forests behind and the springs from which originate the rivers that then flow into the lagoon.