The NE Bommie off Hamelin Island is the most structured reef dive in Hamelin Bay. Marinelife.org.au describes a large bommie about 50 by 50 m in 9-15 m, with submerged caves and swim-throughs, and lists breaksea cod, slender wrasse, western king wrasse, banded sea perch, Port Jackson sharks and stingrays.

A bommie of that size provides a compact dive with plenty of variety: walls around the base, caves and swim-throughs through the middle, and a top at 9 m for a relaxed end to the dive. Port Jackson sharks often rest in caves and under ledges on South West reefs, particularly in the cooler months, and breaksea cod and banded sea perch hang in the shadows.

It suits Open Water divers comfortable with simple swim-throughs, diving from a small boat in good weather. Combine it with the lee reef of Hamelin Island, and finish the day with the stingrays at the ramp.

Hamelin Bay was a timber port from the 1880s, when a jetty built in 1882 and extended in 1898 served M. C. Davies' milling operations. It was notorious for wrecks in bad weather because it is exposed to the north-west gales of winter storms; the 22 July 1900 storm alone wrecked several ships, and only the old jetty piles remain today. The bay is now a recreation zone in the Ngari Capes Marine Park, and every wreck in it older than 75 years is protected. Carry a torch for the caves and look under ledges for resting sharks.

Hamelin Bay is on the coast west of Karridale, about 35 km south of Margaret River and 30 km north of Augusta, reached via Caves Road and Hamelin Bay Road. Park at the boat ramp/jetty area beside the Hamelin Bay Holiday Park. Launch at the Hamelin Bay boat ramp - marinelife.org.au warns it is narrow, slippery and swell-exposed, and a 4WD may be needed.

Run to the north-east side of Hamelin Island and locate the bommie by sounder; boat required, in good weather only.

Boat required in good weather (marinelife.org.au); exposed to north-westerly swell. Calm summer mornings are best. General pattern on the Capes and Leeuwin coast: summer mornings often have light easterly (offshore) winds before a south-westerly sea breeze, and long-period south-westerly groundswell can arrive on otherwise calm days; winter fronts bring big swell and north-westerly winds.

Check the Bureau of Meteorology swell forecast, not just the wind.

Descend onto the bommie, circuit it at 12-15 m, then pass through the caves and swim-throughs before ascending from the top at 9 m. Agree a turn pressure before descending (half gas, or a third where current is likely), carry a DSMB, and make a 3-minute safety stop at 5 m.

No operator; private boats. Nearest dive services: Swan Dive (Busselton/Port Geographe) for fills, hire, nitrox and charters; no dive shop in Margaret River or Augusta.