The Medes Islands ecosystem is deservedly classified as the best natural reserve in the western Mediterranean.
The diversity of depths provides dives for all levels. In the shallow areas we find a dense mantle of well-lit seaweeds and over a hundred brightly coloured species. At depths below 10-15 metres we find light-deprived seaweeds, great rocks surrounded by coral, starfish, gorgonia, octopus and lobster. Below 20 metres we enter a darkness of coral and miniature forests of bright colours inhabited by over 600 species of fauna. The different depths provide diving opportunities for everyone from professional divers to absolute beginners, and all will enjoy the colourful spectacle of underwater marine life.
Numerous caves and tunnels indicate that the limestone archipelago was attached to the Montgrí Massif over ten thousand years ago. Nowadays caves around the Medes Islands and the Montgrí coast provide outstanding opportunities for expert divers: Vaca, Sardina, Dofí Nord caves and Pedrosa tunnel, among others.
Near the islands we find the Reggio Messina, the largest ship that divers can visit on the Costa Brava, sunk deliberately in 1991. The Avenire, also known as the Marmoler, sunk near Cala Montgó cove in 1971 with a cargo of marble in its hold, is the only wholly conserved underwater ship in the area.