Sudbury Reef is a platform reef with a small sand cay lying about 35 km east-south-east of Cairns, south of Fitzroy Island and inshore of the Moore and Briggs reef group. It does not feature on the regular day-trip circuit, and published dive descriptions are scarce, so the account here is based on its geography and on the character of similar mid-shelf reefs nearby. Its value for divers is as a quiet alternative for private charters, sailing groups and private boat owners, who can reach it in a little over an hour from Cairns in fair weather and are unlikely to share it with other boats.

A small sand cay, typical of mid-shelf platform reefs, provides a landmark and a lee on the western side, where the reef edge usually slopes gently from a shallow reef flat into sand at 10-18 m. Expect a mid-shelf coral community of branching, plate and massive hard corals with soft corals in sheltered spots, and fish such as parrotfish, wrasse, damselfish, butterflyfish, coral trout, sweetlips and emperors, with turtles, giant clams and reef sharks likely. Visibility is generally lower than on the outer reefs, typically 8-15 m, and falls after rain.

Divers visiting independently need to be self-sufficient, check the GBRMPA zoning map (much of the reef system around Cairns is zoned Marine National Park or Conservation Park) and use public moorings or anchor only in sand. Its proximity to Fitzroy Island makes it a possible stop on a sailing itinerary.

Boat access only. Cairns day boats leave from the Reef Fleet Terminal (1 Spence Street) and the neighbouring Marlin Marina on the city waterfront, with check-in between about 7:00 and 8:00 am; most operators run transfers from city and northern-beaches accommodation, and there is paid parking near the terminal. The run of about 35 km out through Trinity Inlet and across the lagoon to Sudbury Reef takes around 70 minutes on a fast catamaran and noticeably longer on slower dive boats or into a south-easterly chop.

Sudbury has no regular daily dive operator; it is visited by private charters, sailing trips and private boats from Cairns (Marlin Marina or the Smith's Creek and Tingira Street ramps) or from Yarrabah and Fitzroy Island. Private boaters should use public moorings where available.

The prevailing south-east trade winds (typically 15-25 knots from April to September) are what limit Cairns outer-reef diving: above about 25 knots trips may be cancelled, and exposed eastern moorings are used only in light winds. Summer northerlies are gentler but make north-facing moorings choppy. Box jellyfish and Irukandji are present from about November to May (stinger suits on every dive), and the cyclone season runs November to April, when a system in the Coral Sea can close the reef for days.

Visibility drops after heavy rain and strong winds; spring is usually calmest and clearest. Being closer to the coast, visibility is lower than on the outer reefs, especially after rain. Sudbury is exposed on its eastern side; private boaters should look for the lee of the reef and cay in trade winds and avoid it in winds over about 20 knots.

Anchor or moor in sand in the lee of the reef, descend to the reef edge at 5-8 m and follow it with the reef on one side, turning at half gas. Return shallower along the edge and ascend near the boat.

No regular day-trip operator – private charters, sailing boats and private boats only; Cairns sailing and dive charter boats can include it on private itineraries on request; the mooring used on any day is chosen by the skipper according to wind, tide and other boats