Iceland
A rift-valley diving region in Þingvellir National Park, where fissures between the North American and Eurasian tectonic plates flood the northern shore of Lake Þingvallavatn with glacier-filtered spring water of exce...
Þingvellir, founded as a national park in 1930 and a UNESCO World Heritage Site, sits on the tectonic boundary between the North American and Eurasian plates. Diving takes place in two connected fissures on Lake Þingvallavatn's northern shore, Silfra and Davíðsgjá. Silfra's water is glacial meltwater filtered through lava for 30-100 years, giving visibility reportedly over 100 metres at 2-4 degrees Celsius; regulated dives are capped at 18 m. Source: Wikipedia (Þingvellir, Silfra), Thingvellir National Park official site, DIVE.IS.