Bunaken National Park

Listen first to the water. It slaps softly against the wooden hull of the boat, and the engine drops to a low murmur. Below you, the sea changes colour almost without warning. Deep, ink-dark blue gives way to a pale turquoise glow. That line, sharp as a painted edge, is where the reef begins. On some days you can lean over the side and see coral and fish without ever getting wet.

You are in Bunaken National Park, off the northern tip of Sulawesi in Indonesia. The park was established in 1991. It was one of the country's early marine parks. It covers close to 900 square kilometres, and almost all of that is water. The city of Manado sits on the mainland behind you, and its hills form a green wall at the edge of the bay.

The park takes in five islands. Bunaken is the one that gives the park its name. Manado Tua, Siladen, Mantehage and Nain complete the group. A stretch of mainland coastline to the south also falls under the park's protection. Each island has a different character. Some are low and ringed with sand. Others are wrapped in mangrove. One is a mountain rising straight out of the sea.

That mountain is Manado Tua. The name means Old Manado. It is a dormant volcano, and its cone dominates almost every view in the park. Clouds often gather around the summit while the sea below sits in full sun. Locals say the island was home to some of the earliest settlers in the region. That story is part oral tradition, so take it as part of the island's lore rather than settled history.

Now, here is the first thing many visitors do not expect. The reefs here do not slope gently into the deep. Around Bunaken Island, the coral often grows on vertical walls. A diver can float beside a cliff of living coral, with open blue water at their back. The wall drops away far below, out of sight. This is why divers from many countries come here. Few places offer this kind of wall diving so close to a city.

These waters sit inside the Coral Triangle. That is the name scientists use for a region of ocean between Indonesia, the Philippines, Malaysia, Papua New Guinea and the Solomon Islands. It holds the greatest variety of coral and reef fish found anywhere in the sea. In practical terms, that means a single snorkel can show you dozens of species. Watch for clouds of tiny orange fish, giant clams with bright blue lips, and soft corals that sway in the current.

Green turtles and hawksbill turtles are regular visitors to these reefs. Many snorkellers see one resting on a coral ledge or rising slowly to breathe. Stay calm and keep your distance. A turtle that is not chased will often stay close and carry on feeding. Larger animals pass through the park too. Dolphins sometimes run beside the boats in the channel. Dugongs, the gentle sea cows of tropical waters, have also been recorded in the park.

And now the second surprise. In the late 1990s, scientists confirmed that coelacanths live in the waters of North Sulawesi. A coelacanth is a deep-sea fish with a lineage that goes back hundreds of millions of years. For a long time, people believed it had vanished with the dinosaurs. Then a population turned up off East Africa, and later another here, thousands of kilometres away. You will not see one on a snorkel. They live far deeper. But they share this sea with you.

Bunaken is not a wilderness without people. Villages sit along the shores of the larger islands. Fishing families, small homestays and dive lodges live side by side. You will see wooden outrigger boats pulled up on the sand, washing hung between palms, and children playing in the shallows. Many residents belong to communities from the Minahasa region of the mainland and from the islands to the north. Their daily lives depend on the same reefs that visitors come to see.

Protecting the park is a shared effort. Local communities, government agencies and dive operators work together on reef patrols and mooring buoys. Mooring buoys matter more than they seem. Without them, boats drop anchors onto living coral, and one anchor can break decades of growth. Visitors contribute through the park's entry system, which helps fund this work. When your boat ties up to a buoy instead of anchoring, you are watching conservation in action.

Mantehage, the largest island, shows a different side of the park. Much of its coast is lined with mangrove forest. The trees stand on tangled roots above the water. At low tide you can see the roots clearly, grey and twisted. Mangroves are nurseries for young fish, and they protect the shore from storms. They are quieter than the reefs. You hear birds, the drip of water, and the soft tick of crabs moving through the mud.

The reef faces challenges that every visitor should know. Plastic waste drifts in from rivers and from the wider sea, especially in the rainy months. Warmer ocean temperatures can stress the coral and turn it pale. You can help in small ways. Use reef-safe sunscreen. Never stand on coral or touch it with your fins. Take your rubbish back to the mainland. These habits sound minor, but thousands of visitors make them count.

As the afternoon goes on, the light here changes fast. The sun moves behind Manado Tua and the volcano turns into a dark silhouette. The sea goes from turquoise to silver, then to a deep evening blue. On the beaches, boats come home and the smell of woodsmoke and grilled fish drifts from the villages. It is a good time to sit still on the sand and simply look.

So before you leave, look down once more into the water beside you. Find that edge where pale blue meets deep blue. Below that line, the coral wall keeps falling into the dark, full of life you cannot see from here. Notice the volcano on the horizon, the wooden boats, the voices from the shore. When you travel back toward Manado, turn around for a last look. The islands grow small, but the reef carries on beneath the surface.