The Silfra fissure, is known as one of the top dive sites in the world for two main reasons.
First, the Silfra fissure is actually a crack between the North American and Eurasian continents, meaning that you dive or snorkel right where the continental plates meet and drift apart about 2cm per year.
Silfra is the only place where one can dive or snorkel directly in the crack between two continental plates.
Secondly, the underwater visibility in the Silfra fissure is over 100 meters, which creates an underwater experience that will rarely, if ever, be surpassed. The reasons for this astounding water clarity are twofold: the water is cold (2°C – 4°C year round ) as it is glacial water from the nearby Langjökull and this water is filtered through porous underground lava for 30-100 years until it reaches the north end of Thingvellir lake, seeping out from underground wells. The Silfra water is as pristine as water can get and you can drink it at anytime during your dive or snorkel.