Gili Islands Reefs: Turtles, Biorock and the Slow Return of Coral
Three small islands rise from the Lombok Strait off the north-west coast of Lombok, Indonesia: Gili Trawangan, Gili Meno and Gili Air. None of them has a single car or motorbike - transport runs on bicycles and cidomo horse carts - yet below the waterline the traffic is constant. Green and hawksbill turtles graze the seagrass and coral slopes in numbers that have made the Gilis one of the most reliable places in Indonesia to meet them, while just offshore stand some of the world's best-known coral restoration structures. This is a reef system that has been battered, studied, rebuilt and loved in almost equal measure.
Three islands, one reef system
The Gilis sit close together, separated by narrow channels, and their fringing reefs form a single connected system inside the Gili Matra marine recreation park. Gili Trawangan is the largest and busiest of the three, with the highest concentration of dive centres; Gili Meno, in the middle, is the quietest and the one most visitors associate with turtles; Gili Air lies closest to mainland Lombok and balances a working local community with a mellow dive scene. Because the islands are so compact, dive boats can reach almost any site in a short ride, and many operators rotate freely around all three islands depending on tide and current. The reefs themselves follow a familiar pattern: shallow reef flats and seagrass meadows close to shore, a crest, and then slopes and occasional walls dropping into the strait. That compactness is part of the appeal - in a single day you can drift a wall, hover over restoration structures and finish on a seagrass plateau full of grazing turtles.
Fed by the Lombok Strait
The Gilis owe much of their underwater richness to their position. The Lombok Strait, which separates Bali from Lombok, is one of the main passages of the Indonesian Throughflow, the vast movement of Pacific water toward the Indian Ocean. It is also the classic line of the Wallace Line, the biogeographic boundary that early naturalists drew between Asian and Australasian fauna. For divers, the practical consequence is water movement: tides pushing through the strait generate currents that sweep the Gili reefs with plankton and clean, oxygen-rich water. Most diving here is drift diving, and the current is a feature rather than a nuisance - it feeds the soft corals, keeps visibility generally good and brings pelagic visitors past the reef edges. It also demands respect. Currents can switch and strengthen with the tide, which is why local guides plan entries and exits carefully and why the same site can feel entirely different from one day to the next.
The turtle islands
Ask anyone who has snorkelled the Gilis what they remember and the answer is almost always turtles. Green turtles (Chelonia mydas) are the most commonly seen, cropping seagrass in the shallows or resting on coral ledges, and hawksbill turtles (Eretmochelys imbricata) turn up regularly around sponge-rich patches of reef. Sightings are so dependable that several sites carry names like Turtle Heaven, and many snorkellers meet their first turtle within minutes of leaving the beach on Gili Meno's east side. The turtles here are notably relaxed around people, which is both a delight and a responsibility: local dive centres drill the same etiquette into every guest. Keep your distance, never touch or chase, never block an animal's path to the surface when it rises to breathe. Conservation groups on the islands have long run awareness campaigns and hatchling programmes, and the turtles' tolerance of divers is precisely what makes disciplined behaviour around them so important.
Electric reefs: the Biorock story
The Gilis hold a special place in the history of coral restoration. Around Gili Trawangan in particular, dozens of steel structures stand on the sand and rubble, connected to low-voltage power sources. This is Biorock, also known as mineral accretion technology, developed by architect Wolf Hilbertz and marine scientist Thomas Goreau. A weak electrical current passed through seawater causes dissolved minerals to crystallise onto the steel, coating it in limestone similar to natural reef rock. Coral fragments transplanted onto the structures cement in place and, proponents report, often grow vigorously and cope better with stress. The local organisation Gili Eco Trust, founded through cooperation between island dive operators, has coordinated Biorock installation and maintenance here for many years, making the Gilis one of the largest and longest-running Biorock sites anywhere. Whatever one's view of the method's wider scientific debate, the structures have become dive attractions in their own right: sculptural frames furred with coral, swirling with glassfish and juvenile reef fish, a working experiment you can swim through.
Bleaching, earthquakes and recovery
It would be dishonest to describe the Gili reefs as untouched. Like reefs across Indonesia, they have been hit by coral bleaching during strong El Niño years, when unusually warm water forces corals to expel their symbiotic algae. Earlier decades also left scars from destructive fishing practices before protection and tourism changed the economics of the reef. In 2018, a series of powerful earthquakes struck Lombok, shaking the islands and their tourism industry hard. Each time, the story has continued rather than ended. Corals recolonise rubble fields, restoration projects give recovery a head start, and the turtle and fish populations have proven resilient. Diving the Gilis today means reading this layered history on the reef itself: mature coral heads beside young colonies on restoration frames, rubble slopes slowly binding together, and patches that look as if nothing had ever happened.
Dive sites worth logging
The classic Gili roster covers all experience levels. Shark Point, off Gili Trawangan, is famous for white-tip and black-tip reef sharks resting in sandy gutters, along with turtles and occasional schools of bumphead parrotfish. Halik Reef offers drift dives along coral ridges on Trawangan's north side. Meno Wall drops in tiers festooned with sponges and home to nudibranchs, morays and sleeping turtles. The Bounty Wreck, a sunken pontoon off Gili Meno, has matured into a dense artificial reef at comfortable recreational depths. Off Gili Air, Hans Reef delivers muck-style critter hunting - frogfish, pipefish, shrimp - while deep divers with the right training visit the wreck known locally as the Japanese Wreck, lying well beyond entry-level limits. Snorkellers are equally well served: the shallows between and around the islands, including the celebrated underwater sculpture installation of intertwined human figures off Gili Meno, are accessible straight from shore.
Diving here responsibly
The Gilis' popularity is their pressure point. Choose operators that brief on reef etiquette, support local conservation work and enforce good buoyancy over photo-at-any-cost guiding. Reef-safe sun protection, refusing single-use plastics on the islands and keeping fins well clear of coral all matter more here than in less-visited places, simply because so many people repeat the same actions daily. Give the Biorock structures the same care as natural reef - they are living restoration sites, not climbing frames - and treat every turtle encounter as the privilege it is.
Explore on the map
The Gili Islands are a small dot between Bali and the open Indian Ocean, but underwater they punch far above their size. To see how Shark Point, Meno Wall, Halik Reef and the Biorock gardens fit together around the three islands - and how the Gilis relate to the wider reefs of Lombok and the Coral Triangle - open the interactive map and zoom in on the Lombok Strait. Every site mentioned here has its place, and the map makes the geography of currents, channels and reefs click into focus.