Blue Bay first, the island's only protected marine park and its natural aquarium: 38 coral species, clouds of butterflyfish and water at 25 – 29°C year-round. Get in early (before 9:30 am) from the public beach, swim towards the park buoys and let yourself drift. Glass-bottom boats also offer trips with a snorkelling stop for Rs 400 – 600 per person — pick an operator who moors on the fixed buoys, never anchoring on coral.
On the north coast, Trou aux Biches remains the safe bet: coral heads start 30 metres from shore, opposite the Tamil temple, with clownfish, moray eels and sometimes a playful octopus. Pereybère rounds off the day nicely with its deep bay. Special mention for Pointe aux Piments, more confidential: this is where green turtles come to graze — swimming past one, 50 metres from the beach, is a moment suspended in time. You watch, you never touch, you never chase.
In the west, Flic en Flac lines up kilometres of translucent lagoon. The best sector is opposite the Villas Caroline hotel, where the inner drop-off attracts rich marine life. Absolute caution at the pass south of the public beach: the current pulls out to sea, stay within the marked zone. Further south, the La Preneuse lagoon and Ile aux Bénitiers (reached on excursions, Rs 1,200 – 1,800 with a stop at Crystal Rock) complete a very pretty programme.
Gear can be rented everywhere (Rs 200 – 300 a day for mask and snorkel), but a decent set costs Rs 800 at the Bagatelle Decathlon or in Grand Baie shops — quickly worth it. Add reef shoes against sea urchins and a UV rash guard: at midday the sun cuts through the water and chars unprotected backs. Golden lagoon rules: never stand on coral, never feed the fish, and keep 2 metres from turtles. Local tip: visibility is always better in the morning, before the trade wind raises the chop — and at high tide the lagoon gains a metre of fish.