Milln Reef is a spectacular outer Great Barrier Reef formation 56 km off Cairns, prized for its gin-clear waters, soaring coral bommies, and exceptional biodiversity. The reef is anchored by the famous Three Sisters — three giant coral pinnacles rising from 33 m to within a metre of the surface — plus Whale Bommie, Petaj Mooring, and Swimming Pools, each offering vibrant coral gardens, gorgonian sea fans, and swim-throughs. Snorkelers can drift over shallow bommie tops alongside green sea turtles, white-tipped reef sharks, fusiliers, and parrotfish. With 90% snorkeling suitability and near-perfect coral health ratings, Milln Reef delivers a world-class reef experience accessible only via day-tour or liveaboard.
Milln Reef
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Wave Height 0.2 mSwell Period 6.8 sWind Speed 8.4 knPrecipitation 2.8 mmTidal Phase flood
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Community contribution: submitted by Daniel
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Moderate risk: Marine stingers (box jellyfish / Irukandji)
Stinger season (box jellyfish and Irukandji) in warm coastal waters. Outer reef risk is lower than inshore, but still possible November–May. Tour operators provide stinger suits.
Moderate risk: Stinger season (jellyfish)
Stinging jellyfish (including box jellyfish and Irukandji) are present in warmer months (October to May).
Low risk: Tidal currents
Tidal currents can run through the channels between bommies, especially at the Three Sisters and Whale Bommie. Strongest during spring tides.
Low risk: Boat traffic
Boats and mooring lines at popular dive sites. Snorkelers should stay aware of vessel traffic and mooring pennants near the Three Sisters and Whale Bommie.
Low risk: Sharp coral
Sharp coral bommies and shallow reef edges can cause cuts and scrapes if snorkelers make contact.
Low risk: Shallow Coral Bommies
The Three Sisters bommies rise to just 1 m below the surface. Snorkelers must be cautious to avoid contact with the coral, especially at low tide when the bommies are shallower.
Low risk: Ocean Currents
Seasonal ocean currents can develop around the bommies, particularly during changing tides, which may drift snorkelers away from the mooring area.
Low risk: Marine Stingers
Marine stingers (box jellyfish, Irukandji) may be present in tropical Queensland waters. Tour operators provide stinger suits during the warmer months.
Wildlife Guide
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Gallery
2 photos from the community
Getting in
Snorkel tour
Entry
Milln Reef is located 56 km (35 miles) northeast of Cairns in the Coral Sea. Access is exclusively by commercial tour boat. Day-trip and liveaboard vessels depart from the Cairns Marina (Spence St, Cairns City). The crossing takes approximately 1.5–2 hours.
Parking & facilities
Paid parking available at the Cairns Marina and nearby public car parks along the Cairns Esplanade / Spence Street precinct. Arrive early as spaces fill quickly during peak season (May–October). Some tour operators offer shuttle services from Cairns hotels; check with your operator in advance.
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About this data
- Conditions last evaluated
- Spot data last updated
- Data sources
- Open-Meteo (marine & weather conditions), tide predictions via UTide, community contributors (descriptions, hazards, marine life).
- License
- Spot content licensed under CC BY-SA 4.0. How's the Spot is open source.
Weather & swell ┬╖ Open-Meteo marine & weather APIs Tides ┬╖ UTide harmonic analysis Sea & safety ┬╖ community reports