The location of Iceland on two diverging tectonic plates has resulted in the formation of numerous fissures paralleling the fault line. Often these fissures provide an opening into aquifers of groundwater being filtered through the porous volcanic rock. No studies have been conducted specifically on the biology of submersed fissures, which offer a unique opportunity to study groundwater habitats. The main objective of the project was to explore and geographically and ecologically map groundwater filled fissures in two locations in Iceland, Þingvellir (SW-Iceland) and Kelduhverfi (NE-Iceland). All samples and measurements were acquired by scuba diving. The biological sampling focused on systematically describing the biological diversity in the fissures as well as caverns and caves that are found within them. A special emphasis was put on invertebrate fauna while presence or absence of fish was also noted. The invertebrate samples are still being analysed. Preliminary results show that the invertebrate life in these fissures is diverse, but with chironomidae species dominating. In all fissures studied Arctic charr could be found and in one fissure the groundwater amphipod, Crangonyx islandicus, was found. Previously unknown fissures were discovered during the project. These were measured for the construction of geographical maps.