Boulder City
Boulder City is a dive site in Thailand. It lies within the Mu Ko Similan National Park. The sea floor at the site position lies at about 38 meters. Currents typically run at 0.9 km/h and reach 1.6 km/h on the strongest days. Water temperatures range from 29°C in January to 31°C in May. The typical daily tidal range is about 1.6 m. Species recorded in the area include Lined Bristletooth, Indo-Pacific Sergeant Major, Coral Grouper, Banded Coral Shrimp and Bluespotted Wrasse.
Dive Conditions
Data sources: currents and water temperature from Open-Meteo Marine (CC BY 4.0), hourly model values 2024; seabed depth from the GEBCO 2020 Grid, sampled at the site coordinates (grid resolution about 450 m). Tidal range is the median daily range of modelled sea level from Open-Meteo Marine, hourly values 2024. Protected area boundary from OpenStreetMap contributors (ODbL). Species observations from iNaturalist, checked against the World Register of Marine Species.
Conditions at Boulder City through the year
Sea surface temperature at the site coordinates, averaged per month from hourly model values for 2024. The water is warmest in May at about 31 °C and coolest in January at about 29 °C, a spread of 2.2 degrees across the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 28.9 | 29.2 | 29.8 | 30.7 | 31.1 | 30.0 | 29.4 | 29.4 | 29.0 | 29.4 | 29.6 | 29.0 |
Ocean current at the site runs at a typical 0.9 km/h. In the strongest tenth of the hours modelled for 2024 it reaches 1.6 km/h, which is when entries are normally timed to slack water at the turn of the tide.
The tide moves the water level by a median 1.6 m over a day, and by up to 2.2 m on the largest days of the month. That range drives how much water is exchanged over the reef and when the current turns.
In the open sea off Boulder City, the highest wave of the day exceeded 1.5 m on 15.0 % of days between 2015 and 2024. The roughest month was August (46 % of days), the calmest March (0 %).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 1 | 0 | 1 | 16 | 29 | 43 | 46 | 29 | 12 | 0 | 1 |
The seabed directly under the site coordinates sits at about 38 m. This is a bathymetry grid value with a cell size of roughly 450 m, so it describes the depth of the area rather than the deepest point a dive can reach.
Boulder City lies inside Mu Ko Similan National Park. Protected areas can carry their own rules on entry fees, permits, anchoring and fishing; check the current rules with a local operator before you dive.
How Boulder City compares
These comparisons use only the measured values above, set against the 376 dive sites published on findadive.com. A percentage shows the share of other sites with a lower (or higher) value, so it reads the same way wherever the site is.
| Measure | This site | Compared with all sites | Median in Thailand |
|---|---|---|---|
| Mean water temperature | 29.6 °C | warmer than 67 % of the other 375 sites | 29.7 °C (126 sites) |
| Water temperature in the coolest month | 28.9 °C | warmer than 87 % of the other 375 sites | 28.7 °C (126 sites) |
| Typical current | 0.9 km/h | weaker than 62 % of the other 375 sites | 0.7 km/h (126 sites) |
| Current in the strongest 10 % of hours | 1.6 km/h | weaker than 65 % of the other 375 sites | 1.3 km/h (126 sites) |
| Median daily tidal range | 1.6 m | larger than 62 % of the other 375 sites | 1.6 m (126 sites) |
Water temperature, current and tide from Open-Meteo Marine (CC BY 4.0), hourly model values for 2024 at 8.4933°, 97.6652°. Seabed depth from the GEBCO 2020 Grid. Protected area boundary from OpenStreetMap contributors (ODbL). Wave statistics from ERA5-Ocean via Open-Meteo Marine (contains modified Copernicus Climate Change Service information 2015–2024), daily maximum wave height on a 0.5° grid; land shelter tested against Natural Earth coastlines.
Marine life recorded at this site
Research-grade observations from iNaturalist within about 12 km of these coordinates.
