Kefalonia is balancing on the edge of European continental plate, which means at its west lie some of the deepest waters of Mediterranean while at the East there is a protected, shallow sea that expands from the gulf of Patras to the Acheloos river delta and the Echinades islands archipelagos. The biodiversity in this environment is so huge and important that most of Kefalonian coastline is protected under the Natura 2000 network.

Apart from fish and aquatic life that represents the most of Mediterranean ecosystems, Kefalonia is home to the endangered Monk seal Monachus monachus, the Loggerhead Sea Turtle Carreta carreta, (with Skala and Katelios among the most important hatching shores), but also to Short Beaked Dolphins Deplhinus delfis, Bluefin Tuna Thunnus thynnus, Devil Manta Rays Mobula mobular, while Sperm whales Physeter macrocephalus and Fin whales Balaenoptera physalus are frequent visitors.