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Hotels, dive operators, gear, and how to get here are on the Tulamben location page.
Overview
A sheltered bay on Nusa Penida's northwest coast where a sand-floored channel slides past coral slopes to 30–40 m and a rocky islet at the entrance hides a shallow swim-through cavern. From July to October, cold upwelling off the Lombok Strait pulls Mola alexandrini — the bumphead ocean sunfish, often topping 2 m — up from deep water to reef cleaning stations around 20–40 m, where bannerfish pick parasites from their flanks. The same chilled water can fire abrupt down-currents along the outer channel. Glassy visibility, frequently past 25 m, gives the site its name.
Briefing note
Advanced certification and good buoyancy recommended: down-currents near the channel and depths of 20–40 m for mola sightings make this unsuitable for new divers despite the calm-looking bay. Peak mola season (Aug–Sep) draws crowds and boat traffic. Do not chase or crowd the sunfish — hold position and let them approach the cleaning station. Marine park / mooring fees apply.
What you'll see
5 species curated- seasonalOcean sunfish (bumphead mola)Peak: Jul · Aug · Sep · Oct
- year-roundBannerfish
- year-roundWhitetip reef shark
- year-roundBluespotted ribbontail ray
- rareReef manta ray
Conditions
| Month | Water | Visibility | Current |
|---|---|---|---|
| Jan | 27–29 °C | 12–22 m | mild |
| Feb | 27–29 °C | 12–22 m | mild |
| Mar | 27–29 °C | 12–22 m | mild |
| Apr | 26–28 °C | 15–25 m | mild |
| May | 24–27 °C | 15–30 m | moderate |
| Jun | 21–26 °C | 15–30 m | moderate |
| Jul | 19–25 °C | 15–30 m | strong |
| Aug | 18–24 °C | 15–30 m | strong |
| Sep | 19–25 °C | 15–30 m | strong |
| Oct | 23–27 °C | 15–25 m | moderate |
| Nov | 26–28 °C | 12–22 m | mild |
| Dec | 27–29 °C | 12–22 m | mild |
Season calendar
Peak season highlighted · current month outlined
Gear for this site
Beyond the basic kit- 5mm wetsuit + hood — Lombok Strait upwelling drops water to 18–20 °C through a sharp thermocline in the July–October mola season — far colder than the 3mm most divers bring from Tulamben or Sanur.
- SMB and solid buoyancy skills — Crystal Bay is known for sudden down-currents along the outer channel toward the pinnacle; divers must be able to swim off the reef and signal a drifting boat.
Next step
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