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South Kvarken 
Summary
South Kvarken (Finnish: Ahvenanrauma, Swedish: Södra Kvarken) is the narrowest stretch of sea between Finnish Åland and Sweden, forming a strait connecting the Sea of Åland and the Bothnian Sea of approximately 30 km (18.5 mi) across.
60°08′57″N 19°10′21″E / 60.1492°N 19.1725°E