Divers come for one of the world’s most significant marine reserves, but there’s plenty to do on land too – from hiking trails and beaches to seafood tavernas

Greek divers surface around me shouting about “megalo” groupers. I’m surrounded by enormous grins above the water and big fish below. A happy place to be. A bunch of us, divers and snorkellers, are hanging around Agios Petros reef off the island of Alonissos, and there’s a reason the groupers are big here. The National Marine Park of Alonissos Northern Sporades, established in 1992, is Greece’s largest working marine protected area (MPA) – two bigger MPAs have just been created, but are not yet operational. The protective measures appear to be working, judging by the size, abundance and diversity of marine life – glassy waters teeming with colourful fish and precious shells make swimming here an absolute dream.

For those who like to go deeper, Alonissos is the site of Greece’s first underwater archaeological park and museum – the impressive Peristera wreck , with its giant cargo of amphorae preserved from the 5th century BC. This one is for certified divers descending with accredited local dive centres. I’m with one of those schools, Ikion Diving , but today we’re doing something more accessible. We’re in the village of Steni Vala for the launch of a citizen science project, the Highly Protected Mediterranean Initiative (much more fun than it sounds). Ikion is partnering with the universities of Thessaloniki and the Aegean to offer free snorkelling and diving trips logging native and alien species. I’m worried about my fish ID skills, but the effervescent biologist Katerina Konsta runs a great briefing and we’re given dive slates with images to mark (imparting a childish delight at playing scientist).

Divers come for one of the world’s most significant marine reserves, but there’s plenty to do on land too – from hiking trails and beaches to seafood tavernas

Greek divers surface around me shouting about “megalo” groupers. I’m surrounded by enormous grins above the water and big fish below. A happy place to be. A bunch of us, divers and snorkellers, are hanging around Agios Petros reef off the island of Alonissos, and there’s a reason the groupers are big here. The National Marine Park of Alonissos Northern Sporades, established in 1992, is Greece’s largest working marine protected area (MPA) – two bigger MPAs have just been created, but are not yet operational. The protective measures appear to be working, judging by the size, abundance and diversity of marine life – glassy waters teeming with colourful fish and precious shells make swimming here an absolute dream.

For those who like to go deeper, Alonissos is the site of Greece’s first underwater archaeological park and museum – the impressive Peristera wreck , with its giant cargo of amphorae preserved from the 5th century BC. This one is for certified divers descending with accredited local dive centres. I’m with one of those schools, Ikion Diving , but today we’re doing something more accessible. We’re in the village of Steni Vala for the launch of a citizen science project, the Highly Protected Mediterranean Initiative (much more fun than it sounds). Ikion is partnering with the universities of Thessaloniki and the Aegean to offer free snorkelling and diving trips logging native and alien species. I’m worried about my fish ID skills, but the effervescent biologist Katerina Konsta runs a great briefing and we’re given dive slates with images to mark (imparting a childish delight at playing scientist).

Divers come for one of the world’s most significant marine reserves, but there’s plenty to do on land too – from hiking trails and beaches to seafood tavernas

Greek divers surface around me shouting about “megalo” groupers. I’m surrounded by enormous grins above the water and big fish below. A happy place to be. A bunch of us, divers and snorkellers, are hanging around Agios Petros reef off the island of Alonissos, and there’s a reason the groupers are big here. The National Marine Park of Alonissos Northern Sporades, established in 1992, is Greece’s largest working marine protected area (MPA) – two bigger MPAs have just been created, but are not yet operational. The protective measures appear to be working, judging by the size, abundance and diversity of marine life – glassy waters teeming with colourful fish and precious shells make swimming here an absolute dream.

For those who like to go deeper, Alonissos is the site of Greece’s first underwater archaeological park and museum – the impressive Peristera wreck , with its giant cargo of amphorae preserved from the 5th century BC. This one is for certified divers descending with accredited local dive centres. I’m with one of those schools, Ikion Diving , but today we’re doing something more accessible. We’re in the village of Steni Vala for the launch of a citizen science project, the Highly Protected Mediterranean Initiative (much more fun than it sounds). Ikion is partnering with the universities of Thessaloniki and the Aegean to offer free snorkelling and diving trips logging native and alien species. I’m worried about my fish ID skills, but the effervescent biologist Katerina Konsta runs a great briefing and we’re given dive slates with images to mark (imparting a childish delight at playing scientist).