Koh Bon Wall
Koh Bon is located about 20 kilometers north of Island 9 and features one of the only vertical walls in Thailand. The island has no beaches and is in the shape of a horseshoe. The main dive site is on the southwestern point and consists of a 33 meter wall facing the small cove, and a step-down ridge that carries on to depths of over 45 meters.
Leopard sharks are common on the sandy flats below the wall (particularly on the eastern side). Although the soft corals are not as high-profile as they are in the Similans, the colors of the corals are radically different and include shades of turquoise, yellow and blue, besides the more common pinks and purples. With the angles on the wall, they also offer an ever changing spectrum of colors and make for some great photos around noon.
Koh Bon is one of the better places to see manta rays, almost all year around. This last year featured Mantas almost everyday from mid-December until April. Frequent, but not daily sightings for the rest of the season!
There is also a pinnacle in the bay just to the north of the ridge. It is a deep rock, but if you’re an experienced diver it’s worth the short bottom times you’ll get (especially if you’re on a longer trip). Not all boats visit it and if conditions are not good (like the current is wrong), it’s not worth it. But, if the water is clear, you’re good with your air, and the current is slack, it’s a stunning rock. It looks like a temple built by some ancient culture. It’s larger than Richelieu Rock at the base, and a hard swim. The bottom is over 40 meters deep, and the top only come up to about 18-20 meters. Some amazing little critters are seen here including nudibranchs, pipefishes, pleurobranchs and mantis shrimps.
Diving Depths of 1- 35 meters (1-100 feet), with most time spent on the ridge at 20-25 meters (70-85 feet). Visibility runs about 20 meters (75 feet) but gust of cold water, with associated plankton blooms are not uncommon. Currents can be mild to strong, depending on tides. It is also common to have virtually no current inside the bay but a ripping current on the outside.
Experience level: while beginners can do this site, it is recommended that the diver be intermediate and above due to lack of beaches, potentially strong currents and popularity of the site.