The Vistula Lagoon[a] is a brackish water lagoon on the Baltic Sea roughly 56 miles (90 km) long, 6 to 15 miles (10 to 19 km) wide, and up to 17 feet (5 m) deep, separated from the Gdańsk Bay by the Vistula Spit.

The Polish port of Elbląg used to see a substantial amount of trading traffic on the lagoon, but that declined due to international tensions and silting.

[1] The earliest version of the name of the Vistula Lagoon has been recorded in historical sources by Wulfstan of Hedeby at the end of the 9th Century as Estmere.

Then in 1251 there is a reference to Mare Recens et Neriam and finally in 1288 Recenti Mari Hab, which evidently corresponds with the German "Frisches Haff".

In 1454, King Casimir IV Jagiellon incorporated the region to the Kingdom of Poland upon the request of the anti-Teutonic Prussian Confederation.