A single Diploastrea heliopora colony in this lagoon is reckoned to be close to a thousand years old, and it is still growing. Blue Bay lies on the south-east coast of Mauritius, a shallow bowl of water held between Pointe d'Esny and the runway at Plaine Magnien. The bay was gazetted as a marine park in 1997.
In 2008 its 353 hectares entered the Ramsar list of wetlands of international importance. Seagrass meadows, mangrove fringe and some fifty species of hard and soft coral lie within a few hundred metres of the public beach, which is why Blue Bay snorkeling trip tours never travel far to find their reef.
The water has a documented past. Mahébourg, founded in 1804, stands three kilometres north; the wider bay of Grand Port beyond it saw the naval engagement of August 1810, the only French victory at sea inscribed on the Arc de Triomphe. Fishing pirogues worked these shallows for generations before the park existed. Protection came late and was tested quickly. In July 2020 the bulk carrier MV Wakashio grounded on the outer reef off Pointe d'Esny and released roughly a thousand tonnes of fuel oil. Floating booms and volunteer labour kept the worst of it clear of the park's coral gardens.
Recovery is measured in slow increments. Surveys since have tracked staghorn and brain coral regrowth alongside the return of sergeant major and parrotfish shoals. Île des Deux Cocos, a small leased island, marks the eastern edge of the protected zone; casuarina trees, called filao locally, shade the sand behind the shoreline. Boat access is regulated, anchoring restricted, and motorised watersports excluded from the core area. Excursion snorkeling à Blue Bay, as operators along this coast describe it, therefore runs on glass-bottom hulls and fixed mooring buoys rather than engines over living coral.
That regulation shapes what is bookable here. A Blue Bay Marine Park glass-bottom boat and snorkeling tour stays inside the lagoon and its mooring lines. Wider itineraries — an Île aux Cerfs catamaran cruise, or a five-island speedboat run along the south-east coast — trade reef time for open water, sheltered bays and coastline. The honest choice is between the depth of one lagoon and the breadth of several. Either way, a Blue Bay snorkeling trip tour begins where the reef breaks the swell, and the marine park does the rest.
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