Hin Fai Biorock Dive Site, Koh Tao: Depth & Reef Guide

Hin Fai is the home of Koh Tao's first Biorock electric reef, built by volunteers in late September 2008 under the New Heaven Reef Conservation Program. It lies about 250 m off the Sairee side of the island, in roughly 10 to 16 m of water. If you search for Hin Fai Koh Tao or Biorock Koh Tao, this is the site people mean.

It is not a classic fun dive with big fish. It is a conservation site, and the draw is seeing how an experiment in coral restoration looks in real life. Do not confuse it with Sairee Reef, the fringing reef along the beach.

Hin Fai (Biorock) dive site map

2Biorock dome 1, top ~9 m
3Biorock dome 2, top ~9 m
4Biorock dome 3, top ~9 m
5Biorock dome 4, top ~9 m
6Control dome, unpowered

Usual route: Descend the buoy line to the domes, swim through each in turn, circle the square to look at the coral growth, and ascend slowly over the structures. Drawing based on local dive briefings: approximate, not to scale and not for navigation. Your guide's briefing on the day always comes first.

What is Biorock?

Biorock is a method of growing a reef on a steel frame. A low-voltage current runs through the metal, and dissolved minerals in the seawater build up on the surface as a hard, limestone-like coating. Coral fragments tied to the frames can attach easily, and on Koh Tao they are reported to grow more than 50% faster than normal. They are also said to resist bleaching better.

The idea is simple to picture. Imagine a steel cage underwater with a gentle electrical charge running through it. Over time the minerals harden onto the steel and form a rough surface that coral larvae and tied-on fragments can grip. The metal frame is the skeleton, and the coral does the rest.

Diving Hin Fai: the route

Descend the buoy line to the domes, swim through each one in turn, and circle the square formation to look for coral growth. When you are done, ascend slowly over the structures. It is a relaxed dive at a comfortable depth.

The square layout makes navigation simple. Pick one dome as your starting point and work around the square, so you see every structure. Take your time inside each dome, as the side arch and the top opening give you two ways out. Since the structures are only about 4 m tall, even the tops are well below the surface, and you stay comfortably within the 10 to 16 m range of the site.

Underwater layout

Four large steel domes sit in a rough square, about 12 m apart, in around 13 m of water. Each is about 4 m high and 6 m across. Every dome has an arch in its side and an opening at the top, so you can swim through them and out.

A smaller control dome with no power sits close by. Comparing it with the powered frames shows the difference in coral growth at a glance. Acropora and Pocillopora corals, plus assorted fragments, cover the structures.

The seabed around the domes is not well described, and the exact position of the control dome relative to the others is not confirmed, so treat the map on this page as a simple sketch.

Marine life at Hin Fai

The structures attract reef fish, and studies on the site reported more fish around them than around bare sand, but the species are not well documented. Expect the corals to be the star: look closely at the fragments on the frames and the new growth between them. Do not expect big pelagics. The domes are about learning and watching a reef develop.

It also helps to know what you are looking for. Branching corals of the Acropora and Pocillopora families are the main types on the frames, and they are the species the project has worked with most.

Is it still powered?

A 2012 student study reported that the power converter had been off since October 2011 because of a defect. Whether the domes are energised today is not something we can confirm, so ask a dive centre that works with New Heaven before you go. The structures and the corals on them are still worth a visit either way.

Conditions, tips and safety

Current and visibility are not well documented for this site, so ask your guide on the day. Joining a conservation or coral-ID dive through a dive centre connected to New Heaven gives you the most context.

Look closely at the coral fragments and compare them with the control dome.
The swim-throughs make good photo subjects.
Keep your buoyancy under control inside the arches and avoid touching the steel.