Submarine freshwater springs or vruljas are karst phenomena formed due to geomorphological processes. These geomorphological processes took place under the influence of sea level changes. Submarine freshwater springs are a common occurrence along the east coast of the Adriatic Sea and are the most prominent features in places where mountain ranges rise directly from the sea. They represent submerged pits or springs and are the result of the flow of freshwater under pressure in a karstified coast. There are sieve-type submarine freshwater springs and in them fresh water flows from the seabed through many small openings in the sand. Such submarine freshwater springs are poorly accessible for exploration. Also, there are pit-type submarine freshwater springs that are much larger and more accessible to scientists who can conduct research in them by diving. Pit-type submarine freshwater springs can be found in large numbers on the eastern coast of the Adriatic. The geographical, geological and hydrological properties of the submarine freshwater springs are well known. However, little is known about their biology and biodiversity. The submarine freshwater springs are inhabited by a small number of species and they can be subjected to salinity shock. This salinity shock occurs when suddenly fresh water reaches the underground channels and salinity in springs decreases. The aim of this thesis is to combine the available knowledge about the phenomenon of submarine freshwater springs. In this way, it is possible to get a clear insight into the specificity and exceptional importance of these underwater freshwater sources.