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Alonissos — National Marine Park Diving

Dive the National Marine Park of Alonissos — the largest marine protected area in the Mediterranean. 30 years of protection, monk seals, extraordinary visibi…

Alonissos — Diving Inside the Mediterranean's Largest Marine Protected Area

The National Marine Park of Alonissos Northern Sporades was established by Presidential Decree in 1992 — the first marine park in Greece — and is confirmed by the official Alonissos municipality as the largest marine protected area in the Mediterranean, covering approximately 2,200 km² of sea. Three decades of protection without commercial fishing or trawling have produced the kind of marine ecosystem that no longer exists in most of the Aegean: large grouper and sea bream populations, Mediterranean monk seals (one of the world's most endangered marine mammals — present year-round, rarely sighted), dolphins, and extraordinary water clarity.

Diving inside the park is permitted under regulated conditions, conducted by authorised dive centres on Alonissos. The island's official tourism authority (alonissos.gr) confirms diving tourism as a primary activity. Open Water certification minimum. Marine park rules are strictly enforced — dive only with authorised operators. Best season: May–September. Water temperature: 16–26°C.

Getting to Alonissos

No commercial airport. Ferry from Volos or Agios Konstantinos (mainland) via the Northern Sporades route — approximately 3–4 hours fast ferry. The route stops at Skiathos and Skopelos. Alternatively, fly to Skiathos (JSI) for seasonal European connections. Book ferry via Ferryhopper.

The Marine Ecosystem of Alonissos

Three decades without commercial fishing have allowed the marine ecosystem inside the park to partially recover to pre-industrial baseline levels. Grouper (Epinephelus marginatus) and red scorpionfish are significantly more abundant here than in comparable unprotected Aegean waters. The Mediterranean monk seal (Monachus monachus), with fewer than 700 individuals remaining globally, uses the park's sea caves for pupping and rest — sightings are rare but recorded. Dolphins (common and striped) are frequently encountered on dive boat passages. The combination of healthy fish populations and extraordinary water clarity (visibility regularly 30 m+) makes Alonissos unique among Greek dive destinations for wildlife diving.

The island itself is small and quiet in a way that Skiathos and Skopelos — the more visited Sporades — are not. Patitiri, the main village, has a handful of tavernas, a small waterfront, and a pace of life entirely disconnected from the Aegean summer rush. The Chora (old village) at the top of the hill was destroyed by earthquake in 1965 and rebuilt; its restored stone houses and views across the park are exceptional. Alonissos is a destination for visitors who want the marine park over the beach bar, and there is nothing wrong with that.

The Alonissos marine park has the clearest water of any Greek island dive destination — the combination of limited boat traffic, no commercial fishing, and the protected ecosystem produces visibility regularly exceeding 30 m in the reserve's core zone. The park authority strictly enforces anchoring prohibitions in the core zone; dive boats follow designated routes. Plan 3–5 dive days minimum to make the most of the marine park — the multiple-site boat itinerary that covers the park core, the monk seal observation points (no approach), and the shallow reef requires unhurried pacing. Book early in summer — the limited number of licensed dive boat slots fills quickly.