Kosterhavet National Park

Off Sweden's westernmost point, where the cold, salt-rich waters of the North Sea meet the Skagerrak strait, lies Sweden's only marine national park. Kosterhavet — established in 2009 — protects 38,878 hectares of sea and coastline around the Koster Islands, an archipelago of extraordinary marine biodiversity. Here, species diversity rivals the Mediterranean: cold-water coral reefs, over 6,000 recorded marine species, lobster, langoustine, and the only place in Sweden where true oceanic conditions prevail.

The Marine Landscape

Kosterhavet's marine richness stems from its position. The Kosterrännan (Koster Trench) — a submarine canyon reaching 247 metres — channels deep, oxygen-rich Atlantic water directly to the islands. This inflow brings nutrients, larvae, and species that exist nowhere else along Sweden's coast. The trench creates a marine environment more similar to Norway's outer coast than to the rest of Sweden's west coast.

Cold-Water Coral

The park's most celebrated feature is its cold-water coral reef — the only known coral reef in Swedish waters. Built primarily by the species Lophelia pertusa, these reefs grow in the deep, cold waters of the Koster Trench at depths of 80–200 metres. They develop extremely slowly (roughly 5–25 mm per year) and provide habitat for hundreds of associated species. The reefs are protected from trawling, which had previously damaged deep-sea habitats in the area.

Habitats

The park encompasses a remarkable range of marine habitats within a compact area:

Rocky reefs — Kelp forests and encrusting invertebrates in shallow waters
Soft sediment bottoms — Home to burrowing fauna, including langoustine (havskräfta (Norway lobster))
Seagrass meadows — Zostera marina beds providing nursery habitat for fish
Deep trench — Cold-water coral, sea pens, and deepwater species
Tidal pools — Shore-level pools with anemones, crabs, and small fish

The Koster Islands

The two main islands — Sydkoster (South Koster) (8 km²) and Nordkoster (North Koster) (4 km²) — are car-free and have a permanent population of around 300 people, swelling to several thousand in summer. The islands feel like a different Sweden: open heathland, low granite horizons, weathered fishing huts, and an unhurried pace.

Sydkoster — Larger island; small village, shop, restaurants, and the park's Naturum visitor centre. Connected to Strömstad by regular passenger ferry
Nordkoster — Quieter; reached by boat from Sydkoster. Renowned for its eastern shore, which catches Atlantic swells and has a wilder character
Car-free — Both islands prohibit cars. Transport is by foot, bicycle, or electric buggy

Activities

Kayaking

The Koster archipelago is one of Sweden's finest sea kayaking destinations. Sheltered channels between islands provide calm paddling, while more exposed routes offer a sense of genuine coastal adventure. Rental and guided trips are available in summer.

Diving and Snorkelling

The clarity of North Sea water and the density of marine life make Kosterhavet a premier diving destination in Scandinavia. Dive sites range from shallow kelp forests accessible to snorkellers to deep-wall dives along the Koster Trench. Species frequently encountered include:

Lobster, edible crab, spider crab
Ballan wrasse, pollack, cod
Nudibranchs (sea slugs) — exceptional biodiversity
Soft corals, sea fans, and anemones

Walking

Both islands have well-marked trails across granite headlands, through wildflower meadows, and along shorelines. Birdwatching is excellent, particularly for seabirds and waders during spring and autumn migration.

Seal and Wildlife Boat Trips

Guided boat trips run to outer skerries where harbour seals haul out on rocks. Grey seals are also occasionally seen. Seabird colonies include eider duck, oystercatcher, Arctic tern, and guillemot.

Conservation

Swedish coastline — From Bohuslän granite to Baltic limestone — the geology behind the coast

West coast itinerary — Bohuslän, Gothenburg, and the best of Sweden's western shore