Kosterhavet National Park

Lore & Background

Kosterhavet National Park covers 400 square km and includes the sea and shores around the Koster Islands. It has five entrances, as well as an exhibit and patting aquarium. The park is part of the Skagerrak sea and borders the Norwegian marine park of Ytre Hvaler. The environment is unique to Swedish waters, with over 6,000 marine species identified, about 200 of which cannot be found elsewhere in Sweden. Brachiopod, sponge, and coral larvae are brought in by currents from the Atlantic. Rare seabirds such as Arctic terns and skuas, along with a large population of harbor seals, have their habitat here. Plaice, cod, and sea trout breed in shallower waters closer to the shore. The Kosterfjord is 200 m deep with relatively low temperature (5 to 7 °C) and high salinity (about 35%), and its trench has a maximum depth of 247 m, home to many unique local species.

Reader's Guide

Kosterhavet National Park is significant as Sweden's first national marine park, inaugurated in September 2009. It protects a unique marine environment in the Skagerrak sea, hosting over 6,000 marine species, about 200 of which are found nowhere else in Sweden. The park includes the Kosterfjord, a deep trench with cold, saline waters that support species typically found in the Atlantic. It is also home to Sweden's largest seal colony. Professional fishing is allowed under special regulations, with the waters significant for fishing northern prawn and Norwegian lobster. Fishing is regulated by fishery laws and a 2000 agreement, not by environmental protection laws. The park's five entrances and aquarium provide public access, while its border with Norway's Ytre Hvaler marine park creates a cross-border conservation area. The park's legacy lies in its role as a model for marine conservation in Sweden and its protection of a biodiversity hotspot.

Did You Know?

• Kosterhavet National Park is the first national marine park in Sweden, inaugurated in September 2009.
• Over 6,000 marine species have been identified in the park, about 200 of which are not found elsewhere in Sweden.
• The park is home to Sweden's largest seal colony.
• The Kosterfjord has a maximum depth of 247 m and water temperatures of 5 to 7 °C.

A First for Swedish Waters

Kosterhavet National Park holds the distinction of being Sweden's very first national marine park, officially inaugurated in September 2009. Situated in the Skagerrak sea, it spans roughly 400 square kilometers of water and shoreline surrounding the Koster Islands, though the islands' land areas themselves fall outside the park's boundaries. The park stretches across two municipalities—Strömstad and Tanum—within Bohuslän, part of Västra Götaland County. Its northern edge meets the waters of Norway's Ytre Hvaler marine park, creating a transnational stretch of protected sea. The Swedish name, Kosterhavets nationalpark, translates simply as "The Koster Sea National Park," reflecting its focus on the marine environment rather than terrestrial landscapes. This designation marked a significant shift in how Sweden approached conservation, extending national park status into the open sea for the first time in the country's history.

A Living Laboratory of Marine Species

The waters of Kosterhavet host an extraordinary concentration of marine life, with more than 6,000 species identified to date. Roughly 200 of these are entirely unique to Swedish waters, found nowhere else in the country. The park's position in the Skagerrak makes it a natural corridor: brachiopod, sponge, and coral larvae ride Atlantic currents into these shallows, establishing populations that would not thrive in other Swedish seas. The birdlife is equally remarkable—Arctic terns and skuas, both considered rare in Swedish waters, nest and forage here, while a thriving harbor seal colony represents the largest such gathering in all of Sweden. In the shallower coastal zones, plaice, cod, and sea trout spawn in seasonal cycles that have sustained local fisheries for generations. The sheer density and variety of organisms, from microscopic larvae to large marine mammals, makes the park's environment genuinely unique within Swedish waters.

The Kosterfjord and Its Hidden Depths

Beneath the surface of Kosterhavet lies the Kosterfjord, a dramatic underwater landscape that gives the park much of its ecological character. The fjord plunges to a depth of 200 meters, with its deepest trench reaching 247 meters below the surface. Despite its considerable depth, the water remains cold—typically between 5 and 7 degrees Celsius—and carries a high salinity of approximately 35 percent, conditions that distinguish it sharply from other Swedish coastal waters. These specific physical parameters create a habitat unlike any other in Sweden, sheltering many of the park's locally unique species within the trench and along its slopes. The combination of cold, salty, deep water and the inflow of Atlantic larvae means that organisms found on the fjord floor often have no close relatives anywhere else in Swedish marine ecosystems, making the Kosterfjord a singular geological and biological feature of the region.

Coexistence with Fisheries and Visitors

Unlike many marine protected areas that impose blanket bans on extraction, Kosterhavet permits professional fishing under a specific regulatory framework. The waters are particularly valued for northern prawn and Norwegian lobster, and fishing operations here are governed not by environmental protection statutes but by dedicated fishery laws and a bilateral agreement dating to 2000. This pragmatic approach acknowledges the economic importance of the catch while maintaining sustainable practices. For visitors, the park offers five designated entrances along the coastline, providing structured access to the marine environment. An on-site exhibit and a patting aquarium allow the public to encounter marine life up close, fostering awareness of the thousands of species that call these waters home. The balance between regulated commercial activity and public engagement reflects a conservation philosophy that integrates human use rather than excluding it entirely.