{
  "destination": "greece",
  "name": "Greece",
  "question": "Can you snorkel and dive from a charter boat in Greece, and how warm is the sea?",
  "answer": "Yes: the Peristera ancient wreck off Alonissos can be dived from May to October with a certified diving centre (Advanced Open Water needed), while at Zakynthos boats must keep out of Laganas Bay Zone A in summer and at least 50 m from Navagio's shore, according to secondary sources. The sea averages 15.0 °C in March and 25.9 °C in August (NOAA, 1991–2020 mean at our reference point); by our rule of thumb July to September are the months at 24 °C or more, when a 3 mm shorty is enough, while March calls for a 7 mm wetsuit, or a drysuit for diving.",
  "canonical_url": "https://catamaranindex.com/snorkel-dive/greece/",
  "markdown_url": "https://catamaranindex.com/snorkel-dive/greece.md",
  "destination_url": "https://catamaranindex.com/greece/",
  "best_time_url": "https://catamaranindex.com/best-time/greece/",
  "fishing_url": "https://catamaranindex.com/fishing/greece/",
  "api_url": "https://catamaranindex.com/api/snorkel-dive/greece.json",
  "book_url": "https://catamaranindex.com/go/samboat?dest=greece&pos=api",
  "checked": "2026-10-28",
  "sea_temperature": {
    "unit": "celsius",
    "source": "NOAA OISST v2.1 long-term monthly mean",
    "period": "1991–2020",
    "reference_point": {
      "place": "Ionian Sea between Meganisi, Ithaca and the mainland",
      "lat": 38.375,
      "lon": 20.875
    },
    "note": "NOAA OISST v2.1 long-term mean, 1991–2020, one 1/4° sea cell per destination. It is the sea surface; shallow bays can be warmer and water at depth cooler.",
    "warm_water_threshold_c": 24,
    "months": [
      {
        "month": 1,
        "name": "January",
        "sea_c": 15.9,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "7 mm wetsuit, or a drysuit for diving"
      },
      {
        "month": 2,
        "name": "February",
        "sea_c": 15.1,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "7 mm wetsuit, or a drysuit for diving"
      },
      {
        "month": 3,
        "name": "March",
        "sea_c": 15,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "7 mm wetsuit, or a drysuit for diving"
      },
      {
        "month": 4,
        "name": "April",
        "sea_c": 16.2,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "7 mm wetsuit, or a drysuit for diving"
      },
      {
        "month": 5,
        "name": "May",
        "sea_c": 18.9,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "5 mm full wetsuit"
      },
      {
        "month": 6,
        "name": "June",
        "sea_c": 22.3,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "3 mm full wetsuit"
      },
      {
        "month": 7,
        "name": "July",
        "sea_c": 24.5,
        "warm_water": true,
        "wetsuit_rule_of_thumb": "3 mm shorty"
      },
      {
        "month": 8,
        "name": "August",
        "sea_c": 25.9,
        "warm_water": true,
        "wetsuit_rule_of_thumb": "3 mm shorty"
      },
      {
        "month": 9,
        "name": "September",
        "sea_c": 24.9,
        "warm_water": true,
        "wetsuit_rule_of_thumb": "3 mm shorty"
      },
      {
        "month": 10,
        "name": "October",
        "sea_c": 22.8,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "3 mm full wetsuit"
      },
      {
        "month": 11,
        "name": "November",
        "sea_c": 20.4,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "5 mm full wetsuit"
      },
      {
        "month": 12,
        "name": "December",
        "sea_c": 17.8,
        "warm_water": false,
        "wetsuit_rule_of_thumb": "7 mm wetsuit, or a drysuit for diving"
      }
    ],
    "derived": "warm_water and wetsuit_rule_of_thumb are our rules applied to the NOAA mean; sea_c is NOAA's, rounded to 0.1."
  },
  "wetsuit_rule": "Our rule of thumb for snorkelling, applied to the monthly mean: 28 °C or more: swimsuit or rash vest; 26–28 °C: rash vest or 1–2 mm shorty; 24–26 °C: 3 mm shorty; 21–24 °C: 3 mm full wetsuit; 18–21 °C: 5 mm full wetsuit; below 18 °C: 7 mm wetsuit, or a drysuit for diving. Divers lose heat faster and meet cooler water at depth: go one band thicker. People feel cold differently; this is a guide, not a source's advice.",
  "sites": [
    {
      "name": "Peristera ancient shipwreck (Alonissos underwater museum)",
      "kind": "wreck",
      "where": "Alonissos, Northern Sporades",
      "facts": [
        {
          "text": "Visits are dives booked with a certified diving centre, May to October, with certified guides, down to 25 m; you need an Advanced Open Water certificate. Non-divers can take a virtual dive at the visitor centre in Patitiri.",
          "status": "official",
          "sources": [
            {
              "id": "dive_gr_peristera",
              "name": "Visit Greece (Greek National Tourism Organisation)",
              "title": "Alonnisos underwater museum: the ancient shipwreck of Peristera",
              "url": "https://www.visitgreece.gr/en/experiences/culture/museums/alonnisos-underwater-museum",
              "checked": "2026-10-28",
              "note": "Official tourism board page. Diving by reservation with a certified diving centre (May–October), with certified guides, to 25 m, Advanced Open Water required; virtual dive at the Patitiri visitor centre.",
              "tier": "official"
            }
          ]
        }
      ]
    },
    {
      "name": "National Marine Park of Zakynthos (Laganas Bay)",
      "kind": "marine park",
      "where": "South Zakynthos, Ionian Sea",
      "facts": [
        {
          "text": "ARCHELON, a sea-turtle NGO, wrote in 2019 that navigation is completely prohibited in Zone A from 1 May to 31 October and that speed is limited to 6 knots in the rest of the bay (Zones B and C).",
          "status": "secondary",
          "sources": [
            {
              "id": "dive_gr_archelon",
              "name": "ARCHELON (Sea Turtle Protection Society of Greece)",
              "title": "Collisions of boats with sea turtles continue at Zakynthos National Marine Park",
              "url": "https://archelon.gr/en/news/collisions-of-boats-with-sea-turtles-continue-at-zakynthos-national-marine-park-when-will-fines-be-imposed",
              "checked": "2026-10-28",
              "note": "Conservation NGO news item dated 9 August 2019. Not an official text; the park's own site (nmp-zak.org) refused our connection on 28 Oct 2026.",
              "tier": "secondary"
            }
          ]
        }
      ]
    },
    {
      "name": "Navagio (Shipwreck) Bay",
      "kind": "bay",
      "where": "North-west Zakynthos",
      "facts": [
        {
          "text": "To Vima reported on 2 June 2026 that a Joint Ministerial Decision keeps vessels from approaching or anchoring within 50 m of the shore and bans swimming in the whole cove until 31 October 2026.",
          "status": "secondary",
          "sources": [
            {
              "id": "dive_gr_tovima",
              "name": "To Vima (newspaper)",
              "title": "Zakynthos: Navagio beach access curbs extended through 2026",
              "url": "https://www.tovima.com/society/zakynthos-navagio-beach-access-curbs-extended-through-2026/",
              "checked": "2026-10-28",
              "note": "News report dated 2 June 2026 on a Joint Ministerial Decision in the Government Gazette; we did not read the decision itself.",
              "tier": "secondary"
            }
          ]
        }
      ]
    }
  ],
  "fees": [
    {
      "item": "Peristera guided dive",
      "amount": "Not verified",
      "status": "not_verified",
      "sources": []
    },
    {
      "item": "Zakynthos marine park",
      "amount": "Not verified",
      "status": "not_verified",
      "sources": []
    }
  ],
  "mooring_and_anchoring": [
    {
      "text": "Zakynthos: no navigation in Laganas Bay Zone A from 1 May to 31 October; 6-knot limit in Zones B and C (ARCHELON, 2019).",
      "status": "secondary",
      "sources": [
        {
          "id": "dive_gr_archelon",
          "name": "ARCHELON (Sea Turtle Protection Society of Greece)",
          "title": "Collisions of boats with sea turtles continue at Zakynthos National Marine Park",
          "url": "https://archelon.gr/en/news/collisions-of-boats-with-sea-turtles-continue-at-zakynthos-national-marine-park-when-will-fines-be-imposed",
          "checked": "2026-10-28",
          "note": "Conservation NGO news item dated 9 August 2019. Not an official text; the park's own site (nmp-zak.org) refused our connection on 28 Oct 2026.",
          "tier": "secondary"
        }
      ]
    },
    {
      "text": "Navagio: no approaching or anchoring within 50 m of the shore and no swimming in the cove, until 31 October 2026 (To Vima, June 2026).",
      "status": "secondary",
      "sources": [
        {
          "id": "dive_gr_tovima",
          "name": "To Vima (newspaper)",
          "title": "Zakynthos: Navagio beach access curbs extended through 2026",
          "url": "https://www.tovima.com/society/zakynthos-navagio-beach-access-curbs-extended-through-2026/",
          "checked": "2026-10-28",
          "note": "News report dated 2 June 2026 on a Joint Ministerial Decision in the Government Gazette; we did not read the decision itself.",
          "tier": "secondary"
        }
      ]
    }
  ],
  "diving": [
    {
      "text": "Peristera: only with a certified diving centre and certified guides, Advanced Open Water or higher.",
      "status": "official",
      "sources": [
        {
          "id": "dive_gr_peristera",
          "name": "Visit Greece (Greek National Tourism Organisation)",
          "title": "Alonnisos underwater museum: the ancient shipwreck of Peristera",
          "url": "https://www.visitgreece.gr/en/experiences/culture/museums/alonnisos-underwater-museum",
          "checked": "2026-10-28",
          "note": "Official tourism board page. Diving by reservation with a certified diving centre (May–October), with certified guides, to 25 m, Advanced Open Water required; virtual dive at the Patitiri visitor centre.",
          "tier": "official"
        }
      ]
    },
    {
      "text": "The general Greek rules on recreational diving near antiquities and with or without a dive centre: not verified (we did not read the law).",
      "status": "not_verified",
      "sources": []
    }
  ],
  "visibility": {
    "text": "We found no official or survey source for underwater visibility, so we give no figure. Ask the local dive centre on the day.",
    "status": "not_verified",
    "sources": []
  },
  "not_verified": [
    "The rules of the National Marine Park of Alonissos and Northern Sporades (its site refused our connection).",
    "The Zakynthos park's own zoning text (its site refused our connection), and any park fee.",
    "Greek rules on diving near antiquities and diving without a dive centre.",
    "The price of a Peristera dive.",
    "Underwater visibility."
  ],
  "source_counts": {
    "official": 2,
    "secondary": 2
  },
  "status_legend": {
    "official": "Read in an official text: government, park authority, ministry or official tourism board.",
    "secondary": "From a newspaper, NGO, guide or tour operator; not official.",
    "not_verified": "We could not confirm it. We leave it open rather than guess."
  },
  "caveat": "Park rules change and some are seasonal. Check with the park, the charter base or a local dive centre. The answer, wetsuit column and warm-water flag are our wording and rules applied to labelled facts and NOAA means.",
  "sources": [
    {
      "id": "dive_gr_peristera",
      "name": "Visit Greece (Greek National Tourism Organisation)",
      "title": "Alonnisos underwater museum: the ancient shipwreck of Peristera",
      "url": "https://www.visitgreece.gr/en/experiences/culture/museums/alonnisos-underwater-museum",
      "checked": "2026-10-28",
      "note": "Official tourism board page. Diving by reservation with a certified diving centre (May–October), with certified guides, to 25 m, Advanced Open Water required; virtual dive at the Patitiri visitor centre.",
      "tier": "official"
    },
    {
      "id": "dive_gr_archelon",
      "name": "ARCHELON (Sea Turtle Protection Society of Greece)",
      "title": "Collisions of boats with sea turtles continue at Zakynthos National Marine Park",
      "url": "https://archelon.gr/en/news/collisions-of-boats-with-sea-turtles-continue-at-zakynthos-national-marine-park-when-will-fines-be-imposed",
      "checked": "2026-10-28",
      "note": "Conservation NGO news item dated 9 August 2019. Not an official text; the park's own site (nmp-zak.org) refused our connection on 28 Oct 2026.",
      "tier": "secondary"
    },
    {
      "id": "dive_gr_tovima",
      "name": "To Vima (newspaper)",
      "title": "Zakynthos: Navagio beach access curbs extended through 2026",
      "url": "https://www.tovima.com/society/zakynthos-navagio-beach-access-curbs-extended-through-2026/",
      "checked": "2026-10-28",
      "note": "News report dated 2 June 2026 on a Joint Ministerial Decision in the Government Gazette; we did not read the decision itself.",
      "tier": "secondary"
    },
    {
      "id": "noaa_oisst_ltm",
      "name": "NOAA PSL (NOAA/NCEI OISST v2.1)",
      "title": "NOAA High-resolution Blended Analysis: OISST v2.1 long-term mean monthly sea surface temperature, 1991–2020 (sst.mon.ltm.1991-2020.nc)",
      "url": "https://psl.noaa.gov/thredds/catalog/Datasets/noaa.oisst.v2.highres/catalog.html",
      "checked": "2026-10-28",
      "note": "NOAA's published 1/4° monthly climatology (climo_period 1991/01/01–2020/12/31; every month of every cell we use rests on 30 years). Read on 28 Oct 2026 through PSL's THREDDS point service by scripts/fetch-sst.mjs; we chose one sea cell per destination and rounded to 0.1 °C. Satellite-and-in-situ analysis of the sea surface, not a beach or depth reading.",
      "tier": "official"
    }
  ],
  "attribution": "Cite \"Catamaran Index\" with a link to the canonical_url of the page the figure comes from, and name the original source listed with it.",
  "affiliate_note": "book_url links go through /go/samboat, an affiliate link: Catamaran Index may earn a commission on bookings, at no extra cost to the traveller. It never changes the data."
}