Mao Bay Dive Site, Koh Tao: Depth, Map & Marine Life

Mao Bay (also spelled Ao Mao or Aow Mao) is a sheltered dive site on Koh Tao's east to south-east coast. The reef starts in the shallows at 3 to 5 m and slopes gently down to about 18 to 20 m, covered in granite boulders, coral gardens and patches of sand.

It is one of the easier dives on this side of the island: protected from the prevailing winds, usually calm, and suited to both training dives and relaxed fun diving. Since 2023 it has had an extra draw, because the ex-navy wreck HTMS Hanhak Sattru sits on the sand at the bay mouth.

Mao Bay dive site map

1Shoreline, land to the west
2Shallow coral gardens, 3 to 8 m
3Granite boulders, 6 to 14 m
4Swim-through and overhangs
5Coral bommies, 8 to 16 m
6Sandy patches and slope ~20 m
7Hanhak Sattru wreck, 22 to 24 m

Usual route: Descend at the bay mouth or on the wreck, then follow the slope shoreward across sand and bommies to the boulders and coral gardens, finishing in the shallows. Drawing based on local dive briefings: approximate, not to scale and not for navigation. Your guide's briefing on the day always comes first.

Getting to Mao Bay

Mao Bay is a boat dive. Trips run about 15 to 20 minutes from the pier area, and it is often paired with Shark Island, Aow Leuk, Tanote Bay or the Hanhak Sattru wreck.

Because the east coast is exposed in the north-east monsoon, the bay is dived mostly in the calmer months. In season, many centres use it as a reliable fallback when other sites are rough.

Diving Mao Bay: the route

A typical dive starts at the bay mouth, either on the wreck or on the sand beside it, and works back toward the shore. You follow the slope across sand and coral bommies, then reach the granite boulders and the shallow coral gardens, finishing in the shallows with an easy safety stop.

The profile is gentle, so you spend most of the dive at moderate depth with plenty of time to look around. Divers who start at the wreck get a deeper first half and a long, relaxed ascent.

Underwater layout

Shallow coral gardens: about 3 to 8 m near the shore, ideal for skills and training.
Granite boulders: roughly 6 to 14 m, with small swim-throughs and overhangs, especially toward the sides.
Coral bommies: scattered across the slope at around 8 to 16 m.
Sandy patches: between the coral, where rays rest.
Hanhak Sattru wreck: upright at the bay mouth, 22 to 24 m.

The layout on the map is schematic, so use it as a guide to what is where rather than an exact chart.

Marine life at Mao Bay

The boulders and overhangs hold moray eels, lionfish and groupers, while blue-spotted stingrays settle on the sand. Butterflyfish, angelfish and parrotfish work over the coral, and schools of snapper hang above the reef.

Green turtles drop by from time to time, and trevally and barracuda sometimes pass through. For macro, look for nudibranchs, cleaner shrimp and juvenile reef fish tucked among the rocks.

Mao Bay, the wreck and who it suits

The bay's biggest change in recent years is the HTMS Hanhak Sattru, a former Royal Thai Navy attack craft sunk as an artificial reef in September 2023. It lies at 22 to 24 m, so it is a dive for Advanced divers, but it is usually done as one profile with the bay.

Divers who are not ready for the wreck can still enjoy the shallower reef. Ask your centre which version of the dive is planned.

Mao Bay is a rare site that works for almost everyone in the boat. Trainee divers use the shallow upper reef for Open Water course dives and refreshers, while certified divers spend their time on the deeper outer section of the slope.

Underwater photographers like it too. The calm water, the rays on the sand and the small life hiding among the rocks all reward a slow, patient dive, and visibility is usually best on calm days with little tidal flow.

If you are building a trip around the east coast, Mao Bay pairs naturally with Shark Island, Aow Leuk or Tanote Bay, and it is a sensible plan B whenever the wind has made other sites rough.

Conditions and best time to dive

May to September is the best window, when the south-west monsoon leaves the east coast sheltered. October to December is the north-east monsoon season and the bay can be exposed.

Visibility is typically 8 to 20 m depending on season and tide. Current is generally minimal, apart from some tidal flow near the bay mouth by the wreck.

Tips from local divers and safety notes

Combine the bay with the wreck for a varied dive.
Take time to look into the overhangs for lionfish and morays.
Calm water makes this a good photography site.
Keep your buoyancy tidy around the swim-throughs to protect the coral.
Expect tidal flow near the wreck and variable visibility, and note that boat time depends on sea conditions.