Kosterhavet and Stromstad

June to September is a practical starting window for planning local boat and club diving, while April, May and October are more dependent on cold-water experience and the actual operator. This is not a proven high-visibility season or a guarantee of departures. The Stromstad diving club has a 2026 excursion calendar, but says the listing is under construction and refers visitors to its social channel. Historic Trident seasonal marketing does not establish current schedules. Check SMHI marine conditions, legal site boundaries and a confirmed trip leader before reserving travel.

Ferries leave from Stromstad's north harbour and call at piers on both islands. Kosterlinjen runs services for Vasttrafik; the September 27, 2026 change made line 899 the regular service and added seasonal line 898 serving Ekenas and Kilesand. Depending on your stop and sailing, allow roughly 40 to 60 minutes aboard. Select Ekenas for naturum and the Rorvik area, or the relevant Nordkoster pier for a walking day. Check and purchase through Kosterlinjen and Vasttrafik, especially if your return depends on a late connection.

There are two nationally documented underwater interpretation trails. One lies at Rorvik on Sydkoster, reachable on an island day through the Ekenas area; the other is in Hasslebukten on Salto, reached from the mainland road system. Both are about 200 m long and lie in approximately 1 m to 1.5 m of water, with eight underwater information boards. The park recommends fins, thermal protection in cold water and snorkeling with a companion or shore watcher. Neither site guarantees calm conditions, lifeguards or marine animal sightings. Park trail guidance.

A dedicated local freediving course provider, certified instructor schedule, depth-training line or depth-session product could not be confirmed from the reviewed primary sources through October 28, 2026. Kosterhavet's mapped snorkel routes at Rorvik and Hasslebukten are shallow educational trails, not freediving schools or validated line-training sites. A specialist visitor should independently verify instructor certification, one-up/one-down safety cover, exact site permission, cold-water protocol and rescue provisions before traveling for depth sessions. Do not train alone or regard advertised scuba trips as proof of freedive supervision. Official trail purposes.

Not freely. County prohibitions effective December 19, 2025 cover six legally defined cold-water coral restoration areas, including named locations near Sacken, Grisbardarna, Bjorns rev and Ullvillarna, with other sites at Spiran and Djuprannan. The county says the boundaries were adjusted to exclude popular recreational sites and the protection focuses on deeper coral habitats, but the binding regulations prohibit diving within specified geographical polygons. Nevertheless, location within a designated banned area requires following the legal text, not an assumed depth exception. Review regulations 14FS 2025:31 and 14FS 2025:32 and ask a qualified local operator to verify the exact planned coordinates. County release; Binding prohibition 31; Binding prohibition 32.

The general national park is free to visit, and the naturum Kosterhavet visitor centre has free entry. The reviewed official visitor rules did not establish a universal marine-park dive tag or Koster-specific tourist levy, so no such fee should be invented or collected from this guide. This does not mean every in-water activity or site is unrestricted: protected seabed and wildlife zones, the December 2025 coral diving bans, commercial boat fees and any authorized exemptions still matter. Pay the public-ferry fare separately, and confirm legal access for the exact dive location. County park rules; Tourism overview.

A certification card alone does not establish that a given cold-water site, vessel or dive is suitable for a beginner. The 2026 local club publishes outing and guest price information, but the departure calendar is not a guaranteed public booking list. Trident is included in the 2026 island directory, while current course delivery and equipment availability remain unverified. Ask a current professional operator whether instruction or closely supervised shallow diving is available, what exposure protection is needed, and which specific site is suitable for your recent experience. Club information; 2026 operator listing.

The strongest non-diver plan is a naturum visit at Ekenas, a Rorvik coastal walk and, if time allows, a signed Sydkoster or Nordkoster hiking route. Mainland Salto offers an alternative park entrance for mixed groups that do not want the island ferry. In summer, authorised excursions may head toward Ursholmen lighthouses or look for seals, but these must be booked independently and are weather-dependent. Do not promise a simultaneous dive and boat schedule until each provider confirms times and the correct ferry pier. Park experiences; Regional boat tourism.

No animal encounter should be guaranteed. The national park recommends summer seal-looking excursions from boats, and its seasonal visitor guidance mentions occasional seal and harbour porpoise sightings for autumn kayakers. Neither is evidence of an organized seal swim, whale swim or consistent scuba encounter. Never approach a protected rookery or enter a wildlife buffer for a photograph. The park specifies seasonal protection areas, including a 100 m exclusion at designated seal sanctuaries from May 15 to July 15. Choose a licensed viewing outing and enjoy wildlife only when it appears naturally. Seasonal highlights; Sanctuary rules.

Start with windproof clothing, secure footwear and dry layers, even in summer. For the shallow Rorvik and Hasslebukten trails, bring a fitted mask, snorkel, fins and wetsuit appropriate to actual water temperature, plus a buddy and a warm change afterward. Certified divers should also confirm regulators, suit, gloves, hood, computer, weights, cylinder fills and boat signaling requirements with their provider; do not assume local rentals or Nitrox are available because an older website advertises them. Watch SMHI sea forecasts and the park's snorkeling instructions as your outing approaches.

Treat the train journey as a multi-leg journey rather than assuming a direct uninterrupted service. Sweden's infrastructure authority reports replacement buses on an affected northern Bohus line section to Stromstad from April 20 through December 12, 2026. Other maintenance may affect southern connections as well. Use Vasttrafik's actual date-specific journey planner, allow time for the ferry change at Stromstad Norra Hamnen, and do not depend on superseded printed timetables. For a cross-border alternative, Color Line operates a separate passenger ferry from Sandefjord in Norway to Stromstad, subject to its own check-in conditions. Rail works.

For a suspected diving injury, loss of consciousness, serious breathing problems or a missing diver, activate the emergency plan and call Swedish emergency number 112. Vessels with marine radio can call SWEDEN RESCUE on VHF channel 16. Give the dispatcher the precise location, nature of the dive, number of affected people and available rescue resources, and follow professional instructions. Sweden's 1177 service helps with non-emergency medical advice; local primary care is not a recompression facility. Specialist hyperbaric treatment exists at Ostra Hospital in Gothenburg, but dispatch determines whether and how to transport a patient. Rescue service; Hospital unit.

No. The Koster islands nature reserve has specific overnight restrictions; the main practical public option is the designated campground on Nordkoster, with booking required. The official Lyths rate page lists SEK 230 for a one- or two-person tent pitch in 2026, but this is a dated example rather than a future guaranteed fare. The national park also has special rules for certain smaller islets and anchoring durations, which must not be confused with permission to camp freely on Sydkoster or Nordkoster. Check current maps and booking terms before bringing a tent. Nature reserve rules; 2026 campsite prices.

Yes, provided you choose reasonable walks and verify ferry connections. The Koster islands are generally explored on foot, with cycling permitted on roads under the reserve rules. In summer the Kosterlanken cable ferry is staffed between Nordkoster and Sydkoster; outside that period, passengers can use scheduled Koster boats between relevant piers when times align. Kosterlinjen's September 2026 arrangements also allow bicycles aboard the public ferry free when vessel capacity permits. A one-day itinerary should prioritize a couple of sites rather than assume every path, pier and excursion can be visited. Cable ferry; Updated bicycle carriage.