May through October is the easiest window, with frequent boats, open dive centers, and water that typically ranges from 18°C to 28°C depending on month and latitude. Late spring (May to June) and early autumn (September to October) often feel like the sweet spot: warm water, fewer crowds, and steadier seas. July and August are hot and busy; the Aegean can get strong Meltemi winds, so plan leeward dives like Anthony Quinn Bay or pivot west and south.

For warm, relaxed snorkeling, target June to September when shallow water is often 22°C to 28°C and beach services are fully running. May and October can still be great if you do shorter sessions or wear a light suit, especially in the south. Look for sheltered coves and clear shallows like Agistros or the easy swim lines at Anthony Quinn Bay. In turtle areas, follow marine-park signage and keep respectful distance.

Pick the Aegean for big geology, clear blue, and iconic volcanic sites like Santorini Vulkanwand. It is also more exposed in mid-summer, so wind planning matters. Choose the Ionian for greener coastlines, caves, and often calmer seas, with photogenic coves like Korfu Paleokastritsa Kamelfels and features such as Schwefelhohle Zakynthos. If you are traveling in July or August and want calmer crossings, the Ionian can be the safer bet. For photographers, both regions can deliver 15 m or better on good days.

Most recreational diving is straightforward when you dive with a licensed operator and follow local briefings, but Greece has extra rules around protected areas and underwater cultural heritage. Marine parks can restrict access by zone and season, and some sensitive areas require permission. Around archaeological sites, disturbing or removing anything is illegal, and some visitable sites operate as supervised routes. The simplest approach is to book through a reputable dive center, show your certification, and ask in advance whether your plan includes restricted zones. For ideas, browse the DiveJourney Greece map.

Nesting season is typically May to August, and the priority is giving turtles space. Follow beach access rules (often daytime only) and stay close to the waterline, usually within 5 m of the shore on nesting beaches. Keep your distance from turtles in the water (a good rule is 15 m or more), avoid flash lights at night, and never stand in dunes or dig where nests may be. On boats, go slow in turtle zones and do not anchor on seagrass. Plan your water time around sheltered areas near Schwefelhohle Zakynthos.

Think in clusters. Choose one region (Cyclades, Dodecanese, Ionian, or Crete) and build a loop of short hops, rather than trying to cross the whole country. Use Athens as the main flight gateway, then connect by a single domestic flight or a ferry run to your first base. Aim for 2 to 3 bases over a week and pick dive centers that can run both boat and shore days, so a windy afternoon does not wipe out the schedule. Pack a soft bag and keep buffer time between ferries.

Pack for your month and depth. In peak summer (July to September), water is often 24°C to 28°C, but deeper dives can feel cooler below about 20 m. In May, June, and October, expect more variation (about 18°C to 24°C) and bring warmer exposure if you get cold easily. Winter water can sit near 14°C to 17°C, which is a drysuit or very warm-wetsuit scenario. Booties help on rocky entries, and a windbreaker is useful on boat rides.

Greece is beginner-friendly because many sites are shallow and shore-accessible. Near the capital, 2nd Limanaki offers an easy entry with training-friendly depths. For relaxed island bays, Agistros stays around 7 m to 8 m and is often used for skills practice. Rhodes has calm, protected water at Anthony Quinn Bay. Ask your dive center to match the site to wind, currents, and your comfort with rocky entries.