Kosterfjorden, Marine fjord in Strömstad and Tanum, Sweden
Kosterfjorden is an open marine area between the outer archipelago and the Koster Islands on Sweden's west coast. It runs north to south with varying depths, including a deep channel and shallower muddy zones that create distinct underwater landscapes.
This fjord took shape during the last ice age when glaciers carved deep channels into the Scandinavian bedrock. After the ice retreated thousands of years ago, the sea flooded these valleys to create the waterway we see today.
The name refers to the Koster Islands at the fjord's mouth, which shape the local identity. Fishing communities have worked these waters for generations, adapting their methods to the fjord's distinct zones.
The fjord is visible from several coastal viewpoints in Strömstad and Tanum municipalities. Exploring it by water via boat or kayak provides the best access to different parts of the fjord and its surrounding islands.
This area is Sweden's first marine national park and hosts an extraordinary range of marine life with over 6,000 species. Around 200 of these species are found nowhere else on Earth, making it a globally rare habitat.
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