Iddefjord

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). The outermost stretch is called the Ringdalsfjord, but from the point where it makes a sharp bend and further south, it is called the Iddefjord.

The famous Norwegian fortress Fredriksten in Halden rises over the Iddefjord. The Iddefjord was one of several important geological features that enabled Fredriksten Fortress to successfully repel Swedish invasions in 1716, 1718 and 1814.