One Bum Beach is the gentle counterpart to Barren Island's deep ledges: a small, sheltered fringing reef lying off a tiny beach on the island's protected side. The name is local humour about the size of the beach, and the dive is similarly compact, with the reef sloping from the beach to a sand edge at 6-9 m. The reef is built from plate, branching and boulder corals with patches of soft coral, and it is busy with small tropical fish: damsels, butterflyfish, wrasse, parrotfish and angelfish, plus the odd coral trout and sweetlips sheltering under plates.

Turtles are often seen, and stingrays rest on the sand at the base. Because it is shallow, calm and close to the boat, One Bum Beach is the Keppel operator's choice for a relaxed second dive after Barren's deeper ledges or The Gulch, for divers doing training dives on a longer trip, and for photographers who want long bottom times in good light. The visibility is often better than at the inner islands because of Barren's outer position.

It is not a dramatic dive, and experienced divers may find it quiet, but it is a pretty reef in good health that shows off the range of hard corals found in the eastern Keppels. It suits new Open Water divers, snorkellers staying on the boat, and anyone wanting a low-effort dive to finish the day. As with all the Keppel reefs, conditions on the day matter more than the site itself: after a run of calm weather the water off Barren clears noticeably, while a week of trade winds stirs up sediment even here.

Take a torch to look under the plate corals, where cleaner shrimp and small cryptic fish shelter.

Drive 40 km (about 40 minutes) from Rockhampton to Yeppoon, then 7 km south along the Scenic Highway to Keppel Bay Marina at Rosslyn Bay Harbour, where there is free and paid parking. Freedom Fast Cats and Keppel Konnections ferries run to Great Keppel Island (Fisherman's Beach) in about 30 minutes; Keppel Dive & Water Sports picks up certified divers from the island. One Bum Beach is on Barren Island, about 30-40 minutes by dive boat from Great Keppel or roughly 50 minutes from Rosslyn Bay.

Boats anchor on sand off the beach in the lee of the island; the site is only visited as part of a Barren Island day trip in settled weather.

Keppel Bay is exposed to the prevailing south-east trades (strongest April-September) and to summer northerlies. The beach is on the sheltered side of Barren Island and stays calm in moderate south-easterlies, but reaching it requires a crossing of open water that is uncomfortable above about 15-20 knots. Strong northerlies can send chop into the bay.

Currents are usually slight. Visibility is best July-October and falls after storms or Fitzroy River flood run-off.

Enter from the anchored boat, drop to the sand edge at 6-9 m and follow the reef edge one way for 20-25 minutes, then return along the shallower reef crest in 3-5 m. Finish with a safety stop over the reef top near the boat.

Keppel Dive & Water Sports (PADI 5 Star, based on the Spit at Great Keppel Island next to Great Keppel Island Hideaway) runs guided boat dives to the Keppel sites most days, weather permitting, plus courses and Discover Scuba; site choice is made on the day according to wind. Private boats from Rosslyn Bay also dive here. One Bum Beach is normally the shallow second dive of a Barren Island trip.