Silfra Fissure

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Silfra is a fissure in the Mid-Atlantic Ridge inside Þingvellir National Park (UNESCO World Heritage), where the North American and Eurasian tectonic plates pull apart ~2 cm/year. The water is meltwater from the Langjökull glacier ~50 km north, filtered through porous lava aquifer for 30–100 years before emerging — yielding 2–4 °C, exceptionally clear, and potable. Visibility is among the highest of any natural body of water (commonly reported in the high tens to over 100 m horizontally). Year-round dive — the constant meltwater flow keeps the fissure from freezing — but Sep–Apr surface temperatures and ice make the parking-lot kit-up brutal. Drysuit certification (or 10+ logged drysuit dives) mandatory at all operators. The standard route — Silfra Hall → Cathedral → Lagoon — is a mild downstream drift with a final swim across a shallow lagoon to exit.