Vistula Lagoon
Russia
The Vistula Lagoon is a brackish water lagoon on the Baltic Sea roughly 90 kilometres (56 mi) long, 10 to 24 kilometres (6 to 15 mi) wide, and up to 5 metres (17 ft) deep, separated from the Gdańsk Bay by the Vistula Spit. It is split between Poland and Russia (Kaliningrad exclave).
Data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).