The Iddefjord (a classic fjord with a narrow watercourse and steep natural formations on both sides) runs along the Norwegian – Swedish border from the Singlefjord. The Iddefjord separates the Swedish province of Bohuslän in the county of Västra Götaland from the Norwegian municipality of Halden in the county of Østfold. It opens to the Skagerrak via the Svinesund and Hvaler archipelago (a cluster of classic skerries).