Meet the site
Lost Lake Cave lies on the outer edge of what Extra Divers call one of the largest cave networks on the island. Christmas Island is a raised coral limestone island, and its cliffs are riddled with solution caves; at Lost Lake the system reaches the sea along the base of the north coast cliffs. The 2014 scientific survey of the island's submarine caves (Tan et al.) described Lost Lake as one of the most extensive explorable marine cave systems on the island, highly dependent on tide and wave conditions, with inland anchialine sections that can otherwise only be reached after a walk of three to four kilometres.
The recreational dive is on the outside and in the entrance zone. Extra Divers give a depth range of 11–25 m and describe a unique topography with something new around every corner – undercuts, overhangs, gullies and cave mouths set into the reef and wall. Light streams into the entrances, silhouetting divers against the blue behind, and the shaded ceilings carry sponges, cup corals and sea fans. Outside, the wall and reef hold the usual north-coast life – fusiliers, butterflyfish, triggerfish, groupers and reef sharks – and Extra Divers note whale sharks in season.
The site suits intermediate divers who are comfortable near overhead environments and want more than a straight wall dive. The deep interior of the Lost Lake system is a serious cave and is the preserve of properly trained and equipped cave divers and researchers; recreational groups stay in the daylight zone with a guide.
Lost Lake East, a reef and wall dive nearby, is often dived as a separate site. Together with Thundercliff and Thunderdome to the west, this stretch of coast is the heart of Christmas Island's cave diving.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Lost Lake Cave is recorded as Cave/Cavern in Christmas Island. The listed access is boat. Confirm the actual meeting point, route and permission to visit; a map pin does not establish any of these.
Topics flagged by the stored research
These are questions prompted by the existing notes, not a verified or complete hazard assessment.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
- Overhead environments
- Ask whether the plan stays entirely in open water. A wreck or cave listing is not permission or training to enter.
Historical access notes exist for this record, but have not been independently verified for current use. Request current directions from the operator or site manager rather than following an old entry description.
Questions, answered
Is Lost Lake Cave suitable for my certification?
The record lists Advanced Open Water. That does not establish suitability for every route or day. Share your training, recent experience and equipment needs with the operator and ask about the specific proposed dive.
Can I book Lost Lake Cave through YouDive?
YouDive is an independent research directory. Contact an operator directly to confirm whether it currently runs the trip, the inclusions and the booking terms.
What you might see
Sponges, cup corals and sea fans in the entrances, fusiliers, butterflyfish, triggerfish, groupers, reef sharks, whale sharks (Nov–Apr)
Location
Seaward edge of one of the island's largest submarine cave networks, on the north coast east of Thundercliff Cave.
Facilities nearby
Departs Flying Fish Cove jetty/ramp.
Before you make plans
Conditions, access and operator schedules can change. This is a location guide, not a dive plan. Ask a local operator about current conditions and suitability for your training and experience.
Sources & further reading
extradivers.com.aulkcnhm.nus.edu.sgdiveplanit.comRecord updated 26 Sept 2026. Source claims are being reviewed.