Hamelin Pool

At first sight the shallows of Hamelin Pool look like a field of dark, rounded stones scattered along the shore. They are in fact stromatolites — rock-like mounds built, grain by grain, by communities of cyanobacteria — and they form the most diverse and abundant collection of living marine stromatolites known anywhere. Structures of this kind are among the oldest records of life on Earth: fossil stromatolites near Marble Bar in Western Australia date back about 3.5 billion years, and for a long time such forms were known only as fossils.

That changed here in 1956, when surveyors working for an oil exploration company noticed the mounds at Hamelin Pool and they were recognised as living examples. The reason they survive in this bay is its water. Hamelin Pool, the eastern basin of Shark Bay, is hypersaline, with roughly twice the salinity of ordinary seawater — too salty for most of the marine animals that would otherwise graze on the microbial mats. The bacteria trap fine particles of sand and shell on their sticky surfaces and bind them with calcium carbonate, adding about half a millimetre a year; some columns have reached about 1.5 metres after thousands of years of growth. Scientists estimate that the present formations began building about a thousand years ago. Three broad forms occur: columns that stay permanently submerged, mushroom- and anvil-shaped heads in the tidal zone that are exposed at low water, and flat black microbial mats that look like mudflats.

The bay is named after Jacques Félix Emmanuel Hamelin, the French naval officer who commanded the ship Naturaliste. It is protected as the Hamelin Pool Marine Nature Reserve, covering about 1,270 square kilometres, and lies within the Shark Bay World Heritage Site, inscribed in 1991 and celebrated above all for these stromatolites. A boardwalk was built to let people look at the structures without touching the fragile shore. Beside the shore stands the old Hamelin Pool Telegraph Station, built in 1884, with a post office added two years later.

Getting there

Hamelin Pool lies in the Gascoyne region of Western Australia, about 30 km west of the Overlander Roadhouse on the North West Coastal Highway, reached by Hamelin Pool Road. The nearest city is Geraldton, about 300 km to the south. Shark Bay Airport (MJK), serving Monkey Mia and Denham, is about 43 km away in a straight line on the Peron Peninsula across the water; by road the route runs around the bay via the Overlander Roadhouse and the World Heritage Drive.