In terms of biological diversity, the marine ecosystem of the municipality does not lag behind the terrestrial one.

The blue depths hide biocenoses waiting to be discovered; the coralligenous communities on the underwater walls abound in red algae, multicoloured sponges, crustaceans and soft corals. Semi-dark caves and passages invite you into their labyrinths of tunnels and underwater chambers. There are also green meadows of well-preserved seagrass Posidonia (Posidonia oceanica), a Mediterranean endemic species. Its meadows represent the lungs of the sea, because they enrich the sea with the oxygen they produce. Several hundred species of algae and animals live, breed, hunt and hide in them. With its long leaves, it mitigates the onslaught of waves and prevents the erosion of the shore, while its roots bind the sediment and prevent its removal. 

The biggest underwater attraction of Ližnjan’s seabed is the wreck of "Cesare Rossarol", an Italian scout cruiser that attracts many technical divers. 85 m long and 8 m wide, today she lies at a depth of 50 m near Cape Munat Veliki. She sank in 1918 after running into a moored mine whose powerful explosion halved her in two.

On the south side of the passage to the bay of Kuje, you’ll find Cape Uljeva (Punta Uliva), and in front of it a spacious rocky area with countless rocks that rise from the depth of 5 m almost up to the sea surface. These dangerous shoals were the cause of stranding of many a merchant ship dating back to Roman times. Today, the site abounds with fragmented remains of Roman amphorae that have slept for centuries in ravines and holes between the rocks. It is important to note that these remains are on the List of Preventively Protected Cultural Goods of the Republic of Croatia. Divers often go in search of the remains of the ancient villa of Giulia Frontona, which is believed to have existed in this place.

Best dive sites: Cape Cuf, Cape Sv. Stipan, Sika Rock, Marlera Lighthouse, Cape Uljeva, Cesare Rossarol wreck. They can be visited through excursions organized by the local diving centre Bura Bora.