Meet the site
Blue Lagoon on Thetford Reef is a sheltered lagoon enclosed by coral, with bommies around its margins and shallow sand patches in the middle. Silverswift gives the maximum depth as 18 m with visibility around 10 m, reflecting the calmer, slightly more turbid water typical of lagoons, and it is one of the two Thetford sites Pro Dive Cairns features. It is an easy, forgiving dive. There is no current to speak of, the depth is modest, and the bommies provide constant reference points, so it is ideal for newly certified divers, refreshers and training dives, and for snorkellers who can float over the bommie tops. Giant clams are one of the attractions; Thetford is known for very large specimens and several sit on the lagoon floor. The bommies host butterflyfish, damsels, angelfish, wrasse and parrotfish, with emperors and surgeonfish grazing the margins, and blacktip reef sharks patrol the lagoon, sometimes in the shallows where snorkellers can see them. On the sand look for blue-spotted rays, goatfish and gobies, and in the coral for anemonefish and Christmas tree worms. Because the water is shallow and bright, the site suits photographers, although the visibility is not up to the outer walls. It works well as the final dive of the day or as a night dive in calm weather. Note that Hastings Reef also has a site called Blue Lagoon; the two are unrelated. On a sunny day at high tide the lagoon lives up to its name, with pale sand and clear blue water, and it is one of the best places on the reef for a relaxed, unhurried hour underwater.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Blue Lagoon (Thetford Reef) is recorded as Reef in Cairns. The listed access is boat (day trip). 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.
- Current and timing
- Ask how the operator assesses the current window for the actual route. Historical tide notes are not a departure instruction.
- Other water users
- Ask about vessel activity, exclusion areas and the agreed surface arrangements.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
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 Blue Lagoon (Thetford Reef) suitable for my certification?
The record lists 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 Blue Lagoon (Thetford Reef) 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
Giant clams, blacktip reef sharks, butterflyfish, damselfish, angelfish, wrasse, parrotfish, emperors, surgeonfish, blue-spotted rays, anemonefish, Christmas tree worms
Location
Protected lagoon mooring on Thetford Reef, about 45 km east-south-east of Cairns, ringed by bommies with shallow sand patches.
Facilities nearby
Departs Reef Fleet Terminal / Marlin Marina, Cairns: toilets, cafes, paid parking; dive gear, tanks and lunch supplied on board
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
silverseries.com.auprodivecairns.comcairnsdiveadventures.com.auRecord updated 26 Sept 2026. Source claims are being reviewed.