Lagoon of Szczecin or Bay of Szczecin (Polish: Zalew Szczeciński; German: Stettiner Haff, Oderhaff) is a inland water basin in Poland and Germany situated in the south-western part of the Baltic Sea in the mouth of Oder River north of the city of Szczecin.

It separated from the Bay of Pomerania of the Baltic Sea by the islands of Wolin and Uznam and connected with the 3 straits: Dziwna, Swina and Peene.

Area is 687 sq. km and maximum depth is 6 metres. The lagoon is crossed with a south-north deepened water route with depth of 10 metres connecting the Szczecin seaport via the Oder river with Swina strait, Swinoujscie seaport and the Baltic Sea. This allows large ships to enter the Szczeci seaport.