Otter Reef is one of the outer reefs east of Hinchinbrook Island, beyond the Brook Islands and roughly level with Cardwell. It lies outside the day-trip range of the regular Mission Beach and Townsville operators, and no published dive description exists, so the account here is based on its position and on what is known of neighbouring outer reefs. It is sometimes grouped with Farquharson Reef, a nearby reef in the same area.

As mid-to-outer-shelf reefs away from the mainland river plumes, these reefs would be expected to have clearer water than the inshore islands, typically 12-25 m in calm weather, with healthy hard and soft coral, reef slopes and bommies, and a fish community typical of the central Great Barrier Reef: coral trout, sweetlips, emperors, parrotfish, fusiliers, reef sharks, turtles and giant clams. The area is popular with fishing charters out of Cardwell and Lucinda, so divers are most likely to reach it on a combined fishing and diving charter or in a private boat. Their remoteness means very few divers visit, which is attractive but also means that self-sufficiency, emergency oxygen, communications and a clear evacuation plan are essential, since the nearest chamber is in Townsville.

Zoning varies across these reefs, and some sections may be Marine National Park or Conservation Park zones. Farquharson Reef, sometimes listed alongside Otter Reef, lies in the same area. A calm-weather window, an early start and a well-found boat are the minimum requirements for a visit, and the trip is best planned for the calm spells of September to December.

Otter Reef lies roughly 50 km east of Cardwell. There is no scheduled dive trip: access is by private boat or fishing/dive charter from the Cardwell ramp, Port Hinchinbrook marina, Lucinda or Clump Point (Mission Beach), a run of about 1.5-2 hours in fair weather. Boats must be equipped for offshore travel, and divers need to bring their own gear and fills from Mission Beach or Townsville.

Check the GBRMPA zoning map before fishing or anchoring.

The Mission Beach reefs are exposed to the south-east trade winds, which blow 15-25 knots for much of April-September and can cancel trips; the calmest months are usually September-December. Box jellyfish and Irukandji are present from about October-November to May, most dangerously close to the coast, so wear a full stinger suit. The cyclone season runs November-April, and Mission Beach has been hit hard by cyclones Larry (2006) and Yasi (2011).

Heavy wet-season rain and river flood plumes from the Tully and Johnstone rivers reduce visibility on the inner reefs. The outer reefs off Hinchinbrook have little shelter in fresh trade winds and are realistically dived only in calm spells, usually spring and early summer.

Anchor in sand or pick up a mooring in the lee of the reef, dive the reef edge at 8-18 m with the reef on one side, turning at a third of your gas, and return shallower for a safety stop near the boat.

No regular dive operator – private boats and occasional fishing/dive charters from Cardwell, Lucinda or Mission Beach; Cardwell and Lucinda fishing charters may accommodate divers by arrangement on calm days; the mooring used on any day is chosen by the skipper according to wind, tide and other boats