Szczeciński Lagoon, lagoon (area 350 square miles [900 square km]) on the Baltic Sea coast between Mecklenburg–West Pomerania Land (state), Germany, and Zachodniopomorskie województwo (province), Poland. An extension of the Oder River’s estuarine mouth, it is drained (via the Świna, Peene, and Dziwna rivers) into Pomeranian Bay and the Baltic Sea between Usedom and Wolin.