The waters around and opposite the island, are of great interest, since the underwater wealth is huge - there is considerable marine biodiversity - and the waters remain unexplored. Snorkeling is offered too, for the less daring.
An exciting experience is to dive in the submerged town of Pavlopetri. In 2015, Pavlopetri (and Greece along with it) was included in the top diving destinations of the Mediterranean.
Sources
http://elafonisos.gov.gr
Mentis Sp. Konstantinos Elafonisos Association of Scientists, 2015