Diego Garcia Lagoon

The lagoon of Diego Garcia is one of the largest in the Indian Ocean, covering roughly 1,200 square kilometres and averaging only a few metres depth, a fact that becomes clear only from altitude or from the vantage of a small boat idling over its glassy turquoise surface at dead low tide.

A single narrow opening in the reef on the atoll's eastern side connects the lagoon to the open sea, and the waters inside are typically calm, clear and rich with coral formations that shelter dense populations of parrotfish, giant clams, reef sharks, spotted eagle rays and nesting green turtles.

The surrounding ocean and lagoon were designated a Marine Protected Area by the United Kingdom in 2010, creating one of the world's largest no-take marine reserves at approximately 640,000 square kilometres, though enforcement across such a remote expanse presents obvious challenges.

Historically the atoll was home to the Chagossian people, who were forcibly removed by the British Government between 1968 and 1973 to make way for a joint US-UK military facility, an episode that remains the subject of ongoing legal and diplomatic disputes.

Diego Garcia has long served as a strategic waypoint for dhows sailing between East Africa, the Persian Gulf and Southeast Asia, its sheltered harbour and supply of fresh water making it a natural stop in an otherwise remote ocean; the island itself is about 40 kilometres long and 5 to 8 kilometres wide.

Beyond the military infrastructure and the runway that slices across the atoll's southern tip, the natural landscape retains a primal quality: the interior is dotted with coconut plantations originally established by French colonists in the 18th century, and the shoreline curves in long symmetrical arcs that are visually striking from the air.

The coral reefs ringing the lagoon are regarded by marine biologists as among the healthiest in the Indian Ocean, undisturbed by the coastal development that has degraded coral elsewhere in the region, and they support species including hawksbill turtles, Napoleon wrasse and numerous shark species that are rarely encountered in more heavily fished waters.

The atoll's position at the crossroads of several major ocean currents means that the surrounding waters receive a constant supply of nutrients that sustain the extraordinary productivity of the reef system, and seasonal aggregations of manta rays and schooling barracuda are regular features of the dive sites on the outer reef slope.

The lagoon is also notable for its role in oceanographic research: the 2010 marine protected area designation made the entire Chagos archipelago a reference site for studying reef recovery and fish population dynamics in the absence of fishing pressure, and Diego Garcia's lagoon is one of the key monitoring locations.

The lagoon and its surrounding reefs constitute one of the most intact marine ecosystems in the Indian Ocean, offering exceptional snorkelling and diving in waters that remain largely unpolluted by coastal development.

The atoll's history as a waypoint for Indian Ocean sailing routes gives it a layered human geography, from pre-colonial navigation to 20th-century geopolitics, that is visible in the landscape itself.

The scale of the marine protected area, among the largest in the world, makes the surrounding ocean a genuine refuge for large pelagic species that have been depleted across most of their range.