Vistula Lagoon, Pol. Zalew Wiślany, shallow inlet of the Baltic Sea, 322 sq mi (834 sq km), c.60 mi (100 km) long and from 6 to 11 mi (9.7–18 km) wide, N Poland and W Russia, separated from the Gulf of Danzig by a narrow sand spit. The Nogat and Pregel rivers flow into the lagoon. A dredged channel cuts across the northern end of the inlet and links the Baltic Sea with the Kaliningrad ship canal. The lagoon's shoreline is generally marshy. Kaliningrad is the chief city on the lagoon.