Silfra is a rift formed in the Mid-Atlantic Ridge – the divergent tectonic boundary between the North American and Eurasian plates – and is located in the Thingvallavatn Lake in the Thingvallavatn National Park in Iceland.
Scuba diving and snorkeling in Silfra are popular because of its clear water and location within the continental rift. Silfra is about a 45 to 60-minute drive east of Iceland’s capital Reykjavik. There are three main dive sites: Silfra Hall, Silfra Cathedral, and Silfra Lagoon. The Silfra Hall consists of multiple cave systems underwater with a maximum depth of about 45 metres.The Cathedral is a 100 metres (330 ft) long fissure with visibility almost from end to end. Shallow at the entry points and the ends of the fissure, Silfra descends to a maximum depth of 63 metres (207 ft) but diving to this depth is seldom done as it requires technical diving skills. To get to the main part of Silfra from the caves, divers must go down through the “toilet” headfirst which is a narrow tunnel to a depth of 16 metres. It is the only opening from the Silfra cave to the Silfra crack for the water to go through, thus creating a strong current that flushes every diver straight down. Although this practice is no longer allowed due to the instability of the tunnel, it still holds importance because it is the entrance to the cave. Towards the end of the fissure, it opens up to a shallow lagoon with the most visibility covered in green algae. It is about 120 metres (390 ft) long and is used as the exit point for divers and snorkelers. The water temperature is between 2–4°C (36–39 °F) but can be comfortably dived using a dry suit.