The National Marine Park of Zakynthos was established in 1999 and covers most of Laganas Bay and the southern tip of the island. It is the first marine national park in Greece and one of the most important loggerhead turtle nesting sites in the Mediterranean. The protected zone is divided into three sub-areas, with progressively stricter restrictions on boat speed, anchoring and beach access as you move toward the core nesting beaches at Sekania, Dafni and Marathonisi.
In practical terms, this means motorboats are banned in the inner bay, beaches in the most sensitive zones close at sunset, and only licensed operators are permitted to run turtle-watching trips. The park's information centre at Gerakas on the eastern side of the bay is the best place to start if you want a sense of the science behind the rules — the displays are good and admission is free.