Vistula Lagoon million. However, major ecological considerations stand in the way. For example, mammal migration along the lagoon could be disrupted. Also, the inflow of brackish waters from the Baltic sea could result in serious unbalancing of the lagoon's freshwater ecosystem. From 1772 until 1918, the lagoon was part of the Kingdom of Prussia, which had become part of the German Empire in 1871. Between 1920 and 1946 it was split between Germany and the Free City of Danzig. At present state since 1945 its eastern part belongs to Russia (formerly USSR), Poland has 43.8% of its area at lagoon's western side.
Lagoon coastal transgression and sea level rise. During high flow events there is also the possibility for secondary breaches of the barrier or lagoon truncation to occur. Storm events also have the ability to close hapua outlets as waves overtop the barrier depositing sediment and choking the scoured channel. The resultant swift increase in lagoon water level causes a new outlet to be breached rapidly due to the large hydraulic head that forms between the lagoon and sea water levels. Storm breaching is believed to be an important but unpredictable control on the duration of closures at low to moderate river