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Alam Batu

📍 Bali, Indonesia

Unidentia sandramillenae (Unidentia sandramillenae) — recorded at Alam Batu

Alam Batu is a dive site in Bali, Indonesia. Currents typically run at 0.8 km/h and reach 2.2 km/h on the strongest days. Water temperatures range from 28°C in August to 30°C in November. The typical daily tidal range is about 1.2 m. Species recorded in the area include Peacock Mantis Shrimp, Unidentia sandramillenae, Tryon's Hypselodoris, Crested Nembrotha and Emperor Angelfish.

Dive Conditions

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Current
0.8 km/h (2.2)
🌡️
Water Temp
28–30 °C

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Typical Current 0.8 km/h (up to 2.2)
Water Temperature 28–30 °C
Tidal Range 1.2 m (typical daily)
GPS -8.2309°, 115.5662°

Data sources: currents and water temperature from Open-Meteo Marine (CC BY 4.0), hourly model values 2024. Tidal range is the median daily range of modelled sea level from Open-Meteo Marine, hourly values 2024. Species observations from iNaturalist, checked against the World Register of Marine Species.

Conditions at Alam Batu through the year

Sea surface temperature at the site coordinates, averaged per month from hourly model values for 2024. The water is warmest in November at about 30 °C and coolest in August at about 28 °C, a spread of 2.4 degrees across the year.

Monthly sea surface temperature at Alam Batu (°C)
JanFebMarAprMayJunJulAugSepOctNovDec
29.6 29.4 29.6 30.2 29.7 29.0 28.6 28.0 28.5 29.5 30.4 30.4

Ocean current at the site runs at a typical 0.8 km/h. In the strongest tenth of the hours modelled for 2024 it reaches 2.2 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 1.2 m over a day, and by up to 1.7 m on the largest days of the month. That range drives how much water is exchanged over the reef and when the current turns.

Offshore wave statistics are not shown for Alam Batu: within 10 km of the site there is land in the directions from which 97 % of the larger waves in the area arrive, so open-sea values would overstate the swell at the site itself.

How Alam Batu 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.

Alam Batu compared with all listed sites and with Bali
MeasureThis siteCompared with all sitesMedian in Bali
Mean water temperature29.4 °Cwarmer than 52 % of the other 375 sites29.1 °C (99 sites)
Water temperature in the coolest month28.0 °Ccooler than 64 % of the other 375 sites27.8 °C (99 sites)
Typical current0.8 km/hweaker than 73 % of the other 375 sites3.2 km/h (99 sites)
Current in the strongest 10 % of hours2.2 km/hweaker than 54 % of the other 375 sites5.7 km/h (99 sites)
Median daily tidal range1.2 msmaller than 81 % of the other 375 sites1.5 m (99 sites)

Water temperature, current and tide from Open-Meteo Marine (CC BY 4.0), hourly model values for 2024 at -8.2309°, 115.5662°. 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.

Peacock Mantis Shrimp (Odontodactylus scyllarus)
Peacock Mantis Shrimp Odontodactylus scyllarus A brightly coloured mantis shrimp with a green body, orange legs and striking blue, red and green spots on its raptorial appendages. It lives in a burrow.to 18 cm · 3-40 m · by daysandy or rubble areas near reefs, in self-made burrowsLook for a neat, round burrow entrance; the shrimp often sits at the entrance, watching. (c) portioid, some rights reserved (CC BY) · observation
Unidentia sandramillenae (Unidentia sandramillenae)
Unidentia sandramillenae Unidentia sandramillenae A small, translucent nudibranch with a white-edged mantle and scattered orange spots, often seen crawling on algae.to 2 cm · 5-20 m · day and nightalgae-covered rocks and rubbleLook closely on algae fronds; its pale colour and small size make it easy to miss. (c) portioid, some rights reserved (CC BY) · observation
Tryon's Hypselodoris (Hypselodoris tryoni)
Tryon's Hypselodoris Hypselodoris tryoni A nudibranch with a white body and a network of purple lines, edged in yellow. The gills and rhinophores are orange.to 6 cm · 5-30 m · day and nightsponges on coral reefs and rubble slopesLook for its distinctive colour pattern on sponges, which are its food source; it moves slowly. (c) Rachel Crane, some rights reserved (CC BY) · observation
Crested Nembrotha (Nembrotha cristata)
Crested Nembrotha Nembrotha cristata A large, dark green nudibranch with a distinctive crest of finger-like projections along its back and bright orange gills and rhinophores.to 12 cm · 5-30 m · day and nightcoral and rocky reefs, often on spongesLook for its bright orange gills moving slowly on reef surfaces, especially where its sponge prey grows. (c) Rachel Crane, some rights reserved (CC BY) · observation
Emperor Angelfish (Pomacanthus imperator)
Emperor Angelfish Pomacanthus imperator A large angelfish with bold blue and yellow stripes on its body and a dark mask over its eyes. Juveniles are dark blue with concentric white and blue circles.to 40 cm · 1-70 m · by dayouter reef slopes and channelsOften seen swimming alone. Listen for a distinct clicking sound it makes while feeding. (c) norcalmc, some rights reserved (CC BY) · observation
Humpback Unicornfish (Naso brachycentron)
Humpback Unicornfish Naso brachycentron A large surgeonfish with a prominent hump on the forehead, a long dorsal filament, and a pair of sharp caudal spines.to 70 cm · 5-40 m · by dayouter reef slopes and channelsOften seen in small groups; look for the trailing dorsal filament and the distinctive head profile. (c) rashidchan, some rights reserved (CC BY) · observation
Neon Damselfish (Pomacentrus coelestis)
Neon Damselfish Pomacentrus coelestis A small, intensely blue damselfish with a yellow tail, often seen darting among coral branches.to 9 cm · 1-40 m · by dayouter reef slopes and lagoon patch reefsLook for flashes of blue among branching corals, especially Acropora; it retreats into the coral when approached. (c) Bernard DUPONT, some rights reserved (CC BY) · observation
Red Squirrelfish (Sargocentron rubrum)
Red Squirrelfish Sargocentron rubrum A reddish squirrelfish with silvery-white horizontal stripes along its body and large, dark eyes.to 32 cm · 1-100 m · at nightreef caves, crevices, and under ledgesLook for its reflective eyes in dark recesses during the day; it is more active and easier to spot at night. (c) Bernard DUPONT, some rights reserved (CC BY) · observation