The Iddefjord runs along the Norwegian

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

 – Swedish

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

 border from the Singlefjord. The Iddefjord separates the Swedish province of Bohuslän

Bohuslän

' is a Swedish traditional province, or landskap, situated in Götaland on the northernmost part of the country's west coast. It is bordered by Dalsland to the northeast, Västergötland to the southeast, the Skagerrak arm of the North Sea to the west, and the county of Østfold in Norway to the north...

 in the county of Västra Götaland

Västra Götaland County

Västra Götaland County is a county or län on the western coast of Sweden.The county is the second largest of Sweden's counties and it is subdivided into 49 municipalities . Its population of 1,550,000 amounts to 17% of Sweden's population...

 from the Norwegian municipality of Halden

Halden

is a both a town and a municipality in Østfold county, Norway. The seat of the municipality, Halden is a border town located at the Tista river delta on the Iddefjord, the southernmost border crossing between Norway and Sweden.-History:...

 in the county of Østfold

Østfold

is a county in southeastern Norway, bordering Akershus and southwestern Sweden , while Buskerud and Vestfold is on the other side of the bay. The seat of the county administration is Sarpsborg, and Fredrikstad is the largest city.Many manufacturing facilities are situated here. Moss and...

. It opens to the Skagerrak

Skagerrak

The Skagerrak is a strait running between Norway and the southwest coast of Sweden and the Jutland peninsula of Denmark, connecting the North Sea and the Kattegat sea area, which leads to the Baltic Sea.-Name:...

 via the Svinesund

Svinesund

Svinesund is a sound separating the Swedish municipality of Strömstad in the province of Bohuslän in the county of Västra Götaland from the Norwegian municipality of Halden in the county of Østfold....

 and Hvaler

Hvaler

Hvaler is a municipality that is a group of islands in the southwestern part of Østfold county, Norway. The administrative centre of the municipality is the village of Skjærhalden, on the island of Kirkeøy. The only police station in the municipality is located in Skjærhalden...

 archipelago

Archipelago

An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...

 (a cluster of classic skerries

Skerry

A skerry is a small rocky island, usually defined to be too small for habitation. It may simply be a rocky reef. A skerry can also be called a low sea stack....

). 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

Fredriksten

-History:This Fortresses was constructed ny Denmark-Norway in the 17th century as a replacement for the border fortress at Bohus, which had been lost when the province of Bohuslän was ceded to Sweden by the terms of the Treaty of Roskilde in 1658...

 in Halden

Halden

is a both a town and a municipality in Østfold county, Norway. The seat of the municipality, Halden is a border town located at the Tista river delta on the Iddefjord, the southernmost border crossing between Norway and Sweden.-History:...

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.