Mermaid Reef's Cod Hole is described by Divernet as coral walls and a white sandy base churning with massive bumphead parrotfish, reef sharks, barracuda and trevally, with the current increasing mid-dive for a fast drift exit. Potato cod give the site its name. Mermaid Reef lies within the Commonwealth Mermaid Reef Marine Park, where no fishing is permitted, and has no permanent land.

About the Rowley Shoals: three shelf-edge atolls — Mermaid, Clerke and Imperieuse reefs — rise from 300–700 m depths on the edge of the continental shelf about 260–300 km west of Broome. Mermaid Reef is protected in the Commonwealth Mermaid Reef Marine Park (a no-take national reserve); Clerke and Imperieuse form the State Rowley Shoals Marine Park, with sanctuary zones and limited recreational fishing areas. Clerke carries Bedwell Island and Imperieuse carries Cunningham Island and its lighthouse. More than 200 coral species and 700 fish species have been recorded, and only a few hundred divers visit each year in a season of a few weeks. The 2024–25 marine heatwave hit hard: AIMS surveys in April 2025 found very high (61–90%) coral mortality at Mermaid and Clerke across all habitats to 30 m, so hard coral cover is currently much reduced, although fish, sharks and the drama of the walls and drifts remain.

Planning notes: Advanced Open Water certification is recommended and the site is rated intermediate. Expect to spend most of the dive around 18 m, with a maximum of about 30 m. It can only be reached on a multi-day expedition or liveaboard, so it is usually one of several sites dived on the trip and choices are made by the crew on the day. Currents are significant, so timing around the tide is part of the plan. Best season: September–December (most trips October–November). Traffic: remote/expedition only.

The Rowley Shoals lie about 260–300 km west of Broome and are reached only by liveaboard. Vessels depart Broome (e.g. Odyssey from its depot at 5 Lucas Street) in the evening and steam overnight (about 12–14 hours), spending 5–6 days diving the three atolls before steaming back; typical trips are 6–8 days.

Divers enter from the mothership or from tenders that drop and collect them on drift dives and inside the lagoons, where vessels anchor overnight.

The season is short — roughly September to December (most trips October–November) — when trade winds ease and seas calm between the dry-season easterlies and the cyclone season. Tides of around 4 m drive powerful currents through the atoll channels: drift sites such as Clerke Channel run fast on the flood, and walls and passages are timed by the crew. Inside the lagoons conditions are calm.

Visibility is 20–40 m, sometimes near 60 m, governed by the tide. Water 27–30 °C. Crossings can be rough if the wind is up.

Descend to the sand base at 15–20 m among the coral walls, watch the bumphead schools and sharks, and be ready for the current to pick up mid-dive for a fast drift exit; deploy DSMB for pickup.

Liveaboard only, from Broome: True North (luxury expedition ship), The Great Escape Charter Company (26 m catamaran), Odyssey Expeditions (M/V Odyssey, 24 m catamaran, max 20 guests, 8 days/7 nights, ~26 dives), Diversity Charters (MV Diversity III, 6-day cruises, max 12), plus Ocean Dream Charters and Kimberley Expeditions. Trips book out a year or more ahead.