Peaks in FebRibbontailed StingrayTaeniura lymmaSeen nearby
4%of dives
Elasmobranchii
Photo: Jens Petersen, via Wikimedia Commons · CC BY 2.5 · taken elsewhere
Boat dive · Cave and cavern · Coral
Green Rock
Green Rock, off the northwest side of Koh Nang Yuan near Koh Tao, is a jumble of large granite boulders forming tunnels, caves, arches and swim-throughs among coral.
Also called Green Rock & Red Rock, หินเขียว
- Depth
- 4-32 m
- Level
- Open Water
- Visibility
- 18–30 m
- Water
- 28–31 °C
- Entry
- Boat dive
The verdict
A good dive, worth a day.
Green Rock, off the northwest side of Koh Nang Yuan near Koh Tao, is a jumble of large granite boulders forming tunnels, caves, arches and swim-throughs among coral. Depths run from about 4 m at the top to around 30-32 m at the deepest point.
Titan triggerfish, moray eels, blue-spotted stingrays and turtles are among the regular sightings, with nudibranchs in the crevices. Currents can run through the channels and are sometimes strong, so the maze-like terrain is best suited to divers comfortable with buoyancy and navigation, and some operators ask for an advanced certification.
Location
Map & nearby sites.
Interactive map loads here. Every site on it is also listed on this page.
Right now · updated 12 Nov 2026
November is a good month to dive.
November scores 7.4, against 7.5 in its best months. Live sea readings from NOAA Coral Reef Watch and NOAA WaveWatch III as of 10 Nov 2026.
Water30 °C+1.1° vs normalTick: normal for Nov, 28 °C
Visibility21 mtypical for NovPoor days 18 m · 1 day in 4 is worse
Waves1.2 mModerate6 s period
Reef stressNo stressNOAA Coral Reef Watch heat stress
When to go
Best Jul, Sep-Oct.
Every month gets its own Divegrade score from that month's marine life, visibility, reef and reviews. Across Koh Tao as a whole, the best months are Mar-May.
Divegrade score by monthPick a month for its full guide
Water temperatureSurfaceDive depth28–31 °C
VisibilityBad day to great dayTypical10–34 m
How is this measured?
Mostly from years of satellite readings of how clear the water is around this site. Each bar runs from a bad day, which about 1 day in 10 is worse than, to a great day, which about 1 day in 10 beats; the line marks a typical day. Satellites can't see through cloud, so stormy days are underrepresented and the real bad days can be murkier. For 12 months here, local dive centers report worse days than the satellites see, so the bar starts at their figure. Logged dives will sharpen it over time.
Chance of seeing it on a dive, by monthThe big draws first, then the most frequent. Share of sampled dive days that recorded the species. Months with few dives on record lean on the months around them and the rest of the year, and are shown lighter. A dash means under 1 %.
| Species | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Ribbontailed Stingray | 6 | 8 | 4 | 2 | 2 | 4 | 6 | 4 | 2 | 3 | 6 | 5 |
 Orange-spotted Trevally | 2 | 2 | 1 | 1 | 1 | 3 | 3 | 4 | 9 | 5 | 3 | 2 |
| Redbarred Roccod | 14 | 9 | 8 | 6 | 7 | 13 | 19 | 17 | 27 | 27 | 21 | 19 |
 Yellow Scale Parrotfish | 12 | 9 | 9 | 6 | 5 | 10 | 14 | 16 | 25 | 20 | 17 | 17 |
 Wimple Fish | 9 | 8 | 6 | 5 | 5 | 12 | 20 | 19 | 23 | 15 | 9 | 8 |
 Chocolate Hind | 8 | 6 | 4 | 4 | 5 | 13 | 22 | 17 | 20 | 14 | 9 | 8 |
 Vielle Chocolat | 6 | 5 | 3 | 4 | 5 | 8 | 10 | 12 | 21 | 12 | 7 | 7 |
 Moon wrasse | 8 | 5 | 4 | 4 | 4 | 10 | 15 | 10 | 18 | 19 | 13 | 8 |
 Doublebar Rabbitfish | 8 | 6 | 4 | 3 | 3 | 5 | 7 | 11 | 19 | 8 | 5 | 8 |
 Tattooed Parrotfish | 9 | 5 | 4 | 4 | 5 | 6 | 5 | 7 | 18 | 15 | 13 | 13 |
 Regal Demoiselle | 5 | 3 | 3 | 2 | 3 | 5 | 7 | 8 | 18 | 12 | 6 | 5 |
 Tropical Striped Triplefin | 7 | 5 | 3 | 4 | 5 | 11 | 16 | 13 | 18 | 11 | 6 | 6 |
Marine life
What you'll see at Green Rock.
2.3Big draws. A shark, ray, turtle or other big draw on about 1 dive in 10 in the best months, most often ribbontailed stingray and orange-spotted trevally.
7.3Reef life. Variety: how many different species a few dives here turn up, compared with other sites.
The big draws first (sharks, rays, turtles, octopus and the like) when they turn up on at least 1 dive in 20 in their best month, then the regulars, ranked by how often divers record them across the year. Each percentage is the share of sampled dive days that recorded the species. Where this site has few records of its own, sightings from similar nearby sites (same side of the island, similar depth and exposure) are added at a lower weight and marked "seen nearby".
Peaks in Feb
Peaks in SepOrange-spotted TrevallyFlavocaranx bajadSeen nearby
3%of dives
Photo: portioid, via Wikimedia Commons · CC BY 4.0 · taken elsewhere
Peaks in OctRedbarred RoccodEpinephelus fasciatusSeen nearby
16%of dives
Peaks in SepYellow Scale ParrotfishScarus ghobbanSeen nearby
13%of dives
Photo: no rights reserved, uploaded by steve b · CC0 1.0 · taken elsewhere
Peaks in SepWimple FishHeniochus acuminatusSeen nearby
12%of dives
Photo: (c) Gonzalo Ganda Álvarez, some rights reserved (CC BY) · CC BY · taken elsewhere
Peaks in JulChocolate HindCephalopholis formosaSeen nearby
11%of dives
Photo: portioid, via Wikimedia Commons · CC BY SA 4.0 · taken elsewhere
Photos
4 photos. All from this site.
Divers pick the cover photo. Open any photo and vote for it; the one with the most votes leads this page.
Diver reviews
No reviews yet.
Verified dives count more.
Reviews linked to a logged dive, and reviews from experienced divers, carry more weight in the score.
- 2.5×
- a review backed by a logged dive here, vs. one that isn't
- 2×
- a review from a 100-dive diver, vs. a first-timer's
Dived Green Rock?Sign up free to share how it went. Import your dive log and your review counts as verified.Share how it went. Divers with a logged dive here get the verified badge.
Nobody has reviewed Green Rock yet. Be the first: reviews from divers with a logged dive here count most.
Dive centers
Eight dive centers run Green Rock.
Confirmed: each lists this site on its own website. Listed alphabetically.
| DIVE CENTER | AGENCIES | NITROX | CONTACT | Action |
|---|---|---|---|---|
Big Blue DivingKoh Tao | SSI | Not known | Website+66 77 456 123 | View |
Crystal DiveKoh Tao | SSI | Yes | Website | View |
Dive Center "Scuba Birds"Koh Tao | PADI | Not known | Website+66990307571info@scubabirds.comOSM | View |
French Kiss Divers - ChalokKoh Tao | SSI | Yes | Website+66641276082frenchkissdivers@gmail.com | View |
Hydronauts Diving ResortKoh Tao | RAID | Not known | Website+ 66 080 065 8782OSMinfo@hydronautsdiving.comOSM | View |
Nava Scuba DivingKoh Tao | PADI | Yes | Website+66 77 601198OSMinfo@navascuba.comOSM | View |
Siam Scuba Dive CenterKoh Tao | BSAC, CMAS, NAUI, PADI, RAID, SSI | Not known | Websitesiamscubadivep@gmail.comOSM | View |
The Dearly Dive Koh TaoKoh Tao | PADI, RAID, SSI | Not known | Website+66-(0)77-332-494info@thedearlykohtaohostel.com | View |
Not confirmedEight more centers likely dive here
These centers run trips to sites near Green Rock or are based within 10 km, but their own websites don't name Green Rock. Ask them before you book. Run trips here? Claim your listing and add it.
| DIVE CENTER · WHY LISTED | AGENCIES | NITROX | CONTACT | Action |
|---|---|---|---|---|
Goodtime AdventuresNot confirmed Runs trips to No Name, 750 m away | SSI | Yes | Website+66872753604OSM | View |
KTD - Koh Tao DiversNot confirmed Runs trips to No Name, 750 m away | SSI, TDI | Not known | Website | View |
Dive Poin Koh TaoNot confirmed Runs trips to Twins, 1.3 km away | SSI | Yes | Website+66 77456231OSM | View |
New Heaven Dive SchoolNot confirmed Runs trips to Japanese Gardens, 1.5 km away | SSI | Not known | Website+66 77 457 045info@newheavendiveschool.com | View |
Nang Yuan Easy DiversNot confirmed Based 1.1 km awayOSM | Not listed | Not known | Website | View |
New Way DivingNot confirmed Based 3.7 km awayOSM | Not listed | Not known | Website+66 77 456 527OSMinfo@newwaydiving.comOSM | View |
Apnea TotalNot confirmed Based 4.1 km awayOSM | Not listed | Not known | Website | View |
Rainbow Fish DiversNot confirmed Based 4.4 km awayOSM | Not listed | Not known | Website+66 89-521-7738OSMstefan@rainbowfishdivers.comOSM | View |
OSM From OpenStreetMap (© OpenStreetMap contributors, ODbL), not from the center's own website.
Safety & rules
Know before you drop.
Depth, current and certification are safety calls. This isn't a dive briefing: your guide gives that on the boat or at the entry.
Hazards
No specific hazards recorded. That doesn't mean there are none: ask locally.
Rules and requirements
- Who can dive it
- Open Water Diver (or equivalent), typically to 18 m. Koh Tao sites for Open Water divers
- Local rules
- No specific rules recorded.
- Park fee
- None known
- Depth limits
- The site goes past 30 m, the usual recreational limit. Plan your depth with your guide and set your computer's ppO₂ alarm if you dive nitrox.
- Sources
- Dive center websites, derived, gbif locality, NOAA Coral Reef Watch and NOAA WaveWatch III.
If a diver is hurt: oxygen first, then call for helpFor suspected decompression sickness give 100% oxygen right away and contact local emergency services. DAN emergency hotline: +1 919 684 9111. Check where the nearest recompression chamber is before you travel, and carry dive insurance with evacuation cover.
Questions
When is the best time to dive Green Rock?
July, September, October score highest for Green Rock.
What certification do you need for Green Rock?
Open Water. Open Water Diver (or equivalent), typically to 18 m. Depth 4-32 m.
How we grade
One number, built from dives people actually logged.
- Big draws or varietyMarine life scores the better of two things: how often sharks, rays, turtles and other big draws turn up, and how varied the reef life is, plus a little for having both. Both are per dive, so busy sites can't win on volume.
- By monthEvery month has its own score. Pick a month to see yours.
- Thin data, cautious scoreFew dives or reviews? The score leans toward the regional average.
- Reef healthThe reef score counts coral variety, and recent marine heatwaves that bleach coral take up to 3 points off it, fading over the years after as the reef recovers. Here: the 2024 marine heatwave (peak 7.9 °C-weeks of heat stress), −0.8.
- Hard isn't worseCurrent and depth are shown on their own. A tough site can still score 10.
Sources for this page
Site facts: Dive center websites, derived, gbif locality, NOAA Coral Reef Watch and NOAA WaveWatch III. Occurrence data from GBIF.org; sea conditions from NOAA Coral Reef Watch and Copernicus Marine. Score computed 12 Nov 2026 from 57 logged dives and 0 reviews: medium confidence.
Water temperature: average surface temperature by month from NOAA OISST climatology; at a typical dive depth here from the E.U. Copernicus Marine Service ocean reanalysis. Visibility: NASA satellite water-clarity data, local dive center reports and logged dives.
Photo credits
Blacktip Grouper near Green Rock: (c) portioid, some rights reserved (CC BY), via iNaturalist (CC BY). Orangelined Cardinalfish near Green Rock: (c) portioid, some rights reserved (CC BY), via iNaturalist (CC BY). Eightband Butterflyfish near Green Rock: (c) portioid, some rights reserved (CC BY), via iNaturalist (CC BY). Striped Triplefin near Green Rock: (c) portioid, some rights reserved (CC BY), via iNaturalist (CC BY).