The Chimney, Koh Haa: Vertical swim-throughs and cavern systems

The Chimney is a distinctive reef formation situated on the southern side of Koh Haa Island No. 1 within the Koh Haa group. Unlike the more open, expansive reefs found elsewhere in the Andaman Sea, this site is defined by its complex topography of caverns and swim-throughs. The central feature is a narrow vertical tunnel that begins its descent at approximately 16 to 17 metres. This structure ascends through the reef matrix, eventually opening into various shallower chambers and exits located between 5 and 10 metres deep.

As you navigate the descent, the transition from the open reef to the interior of the chimney offers a significant change in environment. The verticality of the tunnel creates a sense of enclosure that is rare in this region. Once inside the chimney, the water is generally more sheltered from the surge, allowing for a more controlled exploration of the internal structures. You can move between different chambers, using the exits at shallower depths to manage your ascent and observe the light filtering through the reef openings.

Surrounding the central chimney are sloping reef sections and vertical walls that provide a substantial habitat for various marine species. These walls are covered in dense soft coral gardens and patches of typical Andaman hard corals. The depth profile of these surrounding areas ranges from 5 metres down to 30 metres, offering a varied terrain for long, relaxed dives. The contrast between the tight, dark spaces of the chimney and the bright, coral-heavy slopes makes for a highly dynamic dive profile.

The resident fauna is diverse and relies heavily on the protection offered by the reef's architecture. You will frequently encounter groupers and moray eels tucked into the crevices and entrances of the caverns. Smaller reef dwellers like lionfish, scorpionfish, and various species of snappers, damselfish, and fusiliers populate the water column and the coral structures. The presence of these species is often concentrated around the transition zones where the sheltered chimney meets the more exposed reef walls.

Mid-water observations often include larger, more mobile species that patrol the edges of the reef. Trevally and barracuda are commonly seen moving through the blue, often near the edges of the deeper sections of the site. You may also spot green turtles navigating the reef slopes or passing through the shallower areas of the Koh Haa group. These larger animals tend to frequent the areas where the current provides a consistent food source for the smaller reef inhabitants.

Visibility at The Chimney is typically reliable, ranging from 5 to 30 metres depending on the immediate conditions. The light play inside the chimney is a key part of the experience, as sunlight penetrates the narrow openings at shallower depths to illuminate the vertical walls. This lighting effect changes throughout the day, often highlighting the textures of the soft corals and the intricate details of the limestone formations within the upper chambers.

The site serves as a signature dive for the Koh Haa area because it provides an overhead environment that differs from the standard plateau or wall dives. For those who enjoy navigating through swim-throughs and exploring cavernous structures, the site offers a technical interest that is hard to replicate elsewhere in the immediate vicinity. The combination of vertical movement, sheltered internal spaces, and rich coral growth makes it a complex and rewarding site for experienced divers.