Koh Tachai

Descent is on the mooring line, and on a strong-current day it starts the moment your fins hit water: get down fast and use the boulders on the main pinnacle's summit, at 10 to 12 metres, for shelter while you get oriented. From there the dive works around the pinnacle at 18 to 24 metres, following whichever way the current is running that day, through channels between granite boulders scattered across a plateau of hard and soft coral. Divers with air and no-decompression time to spare can cross a sand patch at 24 to 25 metres, a swim of about 50 metres, to a second, smaller pinnacle to the north (whether a further, third pinnacle lies beyond that one is disputed between operators); refuge points thin out on that side, so it suits confident, current-comfortable divers more than a routine extension. The dive typically finishes back on the main pinnacle's summit at around 15 metres, where schooling fish and batfish hold station overhead in the current, so the three minutes of the safety stop pass inside a moving school, not in empty blue.

Most Similan dive sites sit against an island and keep at least some shelter from it. Koh Tachai's Pinnacle has none: a submerged granite dome standing alone in open water, taking the Andaman Sea's current from every direction with nothing to break it. That exposure is the whole point. It is what pulls in the schools: chevron and giant barracuda stacked deep enough to dim the light, giant and bluefin trevally cutting through them, fusiliers moving as one shifting mass around the boulders. Divers who have done the site more than once describe it as unpredictable by nature. A bad day brings poor visibility and a quiet reef, but most days something worth the current shows up. Together with its neighbour Koh Bon, it is the stop some divers rate above "Similan proper," the main archipelago most itineraries also visit. Manta rays add an outside chance on top of the fish action, best from January to May, though never promised.

The reef was in decline before the island closed, worn down by the 2004 tsunami, a 2009 bleaching and warming episode, and severe overcrowding. A 2016 Bangkok Post report put numbers on the last of these: Thon Thamrongnawasawat, deputy dean of Kasetsart University's Faculty of Fisheries, gave the beach's rated capacity as "up to 70 people" against crowds that sometimes ran to "well over 1,000"1. The closure was announced on 15 May 20162 and took effect, with no end date, on 15 October 2016, timed to the park's routine end-of-monsoon reopening date, framed by the department's director-general at the time as protecting a conservation area from tourism-driven damage1. That closure took in the shoreline, beaches and coral reefs around the island, not only its land1. Nine years on, the department's director-general visited the island in April 2025 and reported the environment looking more abundant, with facility construction underway for an eventual, still-undated reopening2. The closure list in force from 1 January 2026 still names Koh Tachai and the coral reef around it as closed indefinitely3.

Advanced Open Water is the minimum here, and one operator's own policy is blunt about it: not appropriate for Open Water divers regardless of logged dive count, with 40 or more dives and some current experience recommended. The working band stays safely inside AOW's 30 metre limit, but the sandy base at the outer edges runs to 35 to 40 metres; treat that depth as a boundary you notice, not a target you swim to. Reach it either as one leg of a Similan-Surin liveaboard, the usual route, or on a dedicated day-trip dive boat from Thap Lamu or Baan Nam Khem pier near Khao Lak, a crossing of a little over an hour each way. There is no snorkelling component at all, since the island's beaches have been shut to visitors since October 2016, so non-diving companions have nothing to do here. A wide-angle lens earns its place; shooting up toward the surface silhouettes the boulders and the fish schools passing overhead. Night dives are not run at the Pinnacle, whose current and remoteness make it unsuitable after dark. The closure that shuts the island also takes in its fringing reef on the eastern side3, and no official text says whether the Pinnacle sits inside it. Operators keep running dives there, so confirm where things stand with your operator or the park office before you book.