- Where
- Hamelin Pool, Shark Bay
Gascoyne, Western Australia - Coordinates
- 26.4028° S
114.1631° E - Biome
- Hypersaline marine embayment
- Salinity
- About twice that of open seawater
- How old
- The lineage runs to c. 3.5 billion years;
a metre-high column, several thousand - Status
- Marine Nature Reserve, within the
Shark Bay World Heritage Area, 1991 - Best visited
- April–October, at very low tide
Drove a long way to look at some grey lumps in very salty water, which is what they are, and stood there for an hour anyway. Somebody explained what they had done and roughly when, and I found myself thanking them out loud, which the other visitors did not comment on. The water fizzes. That is them, still working.
The short answer
Hamelin Pool is a shallow, enclosed arm of Shark Bay on the coast of Western Australia, and one of only two places on Earth where marine stromatolites grow in real abundance — the other being the Bahamas. Stromatolites are not individual organisms. They are layered, rock-like structures built by mats of cyanobacteria, which trap and bind sediment and then grow up through it toward the light, adding a layer at a time. The lineage goes back roughly three and a half billion years, and for most of that span it was the dominant form of life on the planet. Hamelin Pool sits inside the Shark Bay World Heritage Area, inscribed by UNESCO in 1991.
Why it's worth knowing
These are the organisms that made the atmosphere.
Before cyanobacteria, the air held around one per cent oxygen. Photosynthesising microbial mats then spent something like two billion years releasing oxygen into the oceans — the ocean absorbed it, then the ocean saturated, and the surplus went into the air. What is now roughly twenty per cent oxygen, and every animal that has ever breathed, follows from that. You can still watch it happening: on a bright day the stromatolites at Hamelin Pool visibly fizz, letting go of bubbles.
And here is the part that is genuinely strange.
Stromatolites were once everywhere. They dominated the shallow seas of the world for well over a billion years. What ended them was the thing they had made possible: once there was enough oxygen for animals, animals evolved, and animals eat microbial mats. Grazing removed stromatolites from almost every coastline on Earth.
Hamelin Pool is one of the few places they were not reached. A bank of seagrass across the entrance restricts the flow of water in and out, evaporation does the rest, and the pool has become about twice as salty as open seawater. Almost nothing can live in it — certainly nothing that grazes. The oldest form of life on the planet survives in the one condition harsh enough to keep its descendants out.
They will not impress you at a glance. Visitors regularly describe them as looking like cowpats, or like somebody dropped a load of old bricks in the shallows and drove off. That is accurate, and it is beside the point. What you are looking at is the oldest thing alive, doing the job that made you.
The field notes
How a rock grows
A stromatolite is built rather than born, and the mechanism is worth understanding because it explains the shape.
Cyanobacteria form a sticky mat on the sea floor. Sediment settles on it and gets trapped. The mat is now buried and cut off from sunlight, which it needs, so it grows upward through the sediment to reach the light again — forming a new living layer on top of the old one. Then sediment settles again. Repeat, for a very long time.
The result is a domed or cauliflower-shaped column of thin laminations, of which only the top few millimetres are alive. Everything below is the hardened remains of previous mats. A column a metre high may represent several thousand years of that cycle.
So the object in front of you is simultaneously a living organism and its own fossil record, stacked.
Why here, and almost nowhere else
The geography is doing all the work.
Hamelin Pool is nearly cut off from the rest of Shark Bay by a bank of dense seagrass, which restricts tidal exchange. The water that does enter sits in a shallow basin in a hot, dry climate and evaporates faster than it is replaced. The salt stays. Salinity settles at roughly double that of normal seawater.
Bush Heritage Australia notes that only two well-developed marine stromatolite areas exist anywhere — here and in the Bahamas — and that Hamelin Pool is the more extensive and diverse of the two.
The dependence on that seagrass bank is also the vulnerability. Seagrass meadows in Shark Bay have been damaged by flood runoff and marine heat events, and if the barrier degrades, the pool circulates, the salinity falls, and the grazers arrive. The thing that has protected these colonies is not the reserve boundary. It is the salt, and the salt depends on plants.
What you can actually see, in 2026
Most published accounts of Hamelin Pool describe walking out over the stromatolites on a 200-metre boardwalk. That boardwalk has been closed since 2021, when Cyclone Seroja damaged it, and the microbial mats are far too fragile to be walked on directly.
A rebuild has been reported at around $4.6 million, with work described as scheduled to begin in 2026. Whether it has begun, and when it will reopen, should be checked with the Western Australian parks authority before travelling — this entry does not assert a reopening date.
In the meantime the stromatolites are viewed from the shoreline, which is a less satisfying experience and still a remarkable one. Go at very low tide, when more of the colonies stand clear of the water, and bring binoculars or a long lens. From the car park it is about 750 metres on compacted gravel.
Beside the reserve stands the Hamelin Pool Telegraph Station, built in the late nineteenth century to connect Shark Bay to the rest of the world, and now a small museum. It is worth twenty minutes, and there is a certain symmetry in a nineteenth-century communications relay sitting next to the oldest living thing on the coast.
A bay that qualified on every count
Shark Bay is one of a small number of World Heritage sites inscribed against all four natural criteria — for its earth history, its ongoing ecological processes, its natural beauty, and its biodiversity. The stromatolites carry a good deal of that weight, but they are not alone.
The bay holds one of the largest seagrass meadows on Earth, a dugong population in the thousands, and Shell Beach, where the beach is not sand at all but coquina — billions of tiny shells of a single cockle species that thrives in the hypersaline water, packed metres deep and, further inland, quarried in blocks as building stone.
The same salt that preserves the stromatolites produced a beach made of shells and a town partly built out of it.
- Come at the lowest tide of the day, not the most convenient one.
- Bring binoculars. From the shore, they are a grey smudge without them.
- Read the signs before looking, not after.
- Go to Shell Beach afterwards and pick up a handful.
- Say thank you. It is not silly. They earned it.
A block of shell. At Shell Beach the coquina compacts into a solid mass that can be cut in slabs, and buildings in Denham are made of it — walls of nothing but tiny shells, cemented by time. It is a building material produced by the same salinity that keeps the stromatolites alive: one condition, two entirely different consequences, forty kilometres apart.
Tally, in the marginA wall made of nothing but shells, held up by time. The same salt did both of these things and I cannot stop thinking about it.
Getting there
How to get there. Hamelin Pool is about 800 km north of Perth, roughly nine hours by road, and 27 km off the North West Coastal Highway on Shark Bay Road. Most visitors come as part of a Shark Bay trip taking in Denham, Monkey Mia and Shell Beach. There is no public transport; this is a self-drive or organised-tour destination.
Check the boardwalk before you commit. It has been closed since Cyclone Seroja in 2021 and a rebuild has been reported as scheduled to begin in 2026. Confirm current access with the Department of Biodiversity, Conservation and Attractions rather than relying on travel articles, most of which still describe walking out over the water.
Time it with the tide. The stromatolites are best seen at very low tide, when the colonies stand proud of the water. At high tide from the shoreline you will see very little. Tide tables matter more here than time of day.
When to go. April to October. Summer in the Gascoyne is severe, and the walk to the viewing area is exposed with no shade.
What to bring. Binoculars or a telephoto lens, which turn a distant grey lump into a visibly layered structure. Water. Sun cover. And realistic expectations, followed by the interpretive signs, in that order — this is a place that rewards understanding rather than looking.
Do not walk on them. The mats are destroyed by footfall and do not recover on any timescale that means anything.
Mark this place
Common questions
What are the stromatolites at Hamelin Pool?
They are layered, rock-like structures built by mats of cyanobacteria — not individual organisms but colonies. The microbes trap and bind sediment, then grow upward through it toward sunlight, adding a living layer on top of the old one. Repeated over centuries this builds domed columns of which only the top few millimetres are alive.
Why are stromatolites important?
Because they made the atmosphere breathable. Before cyanobacteria the air held around one per cent oxygen. Photosynthesising microbial mats released oxygen into the oceans for roughly two billion years; once the water saturated, the surplus entered the air. The roughly twenty per cent oxygen that animal life depends on follows from that process.
Why do stromatolites survive at Hamelin Pool and almost nowhere else?
Because the water is too salty for the animals that would eat them. A seagrass bank across the entrance restricts tidal exchange, and evaporation in a hot dry climate raises salinity to about twice that of open seawater. Grazing animals eliminated stromatolites from most of the world’s coastlines; here they cannot survive to do so.
Where else in the world can you see living marine stromatolites?
Only one other place has them in comparable development: the Bahamas. Bush Heritage Australia describes Hamelin Pool as the more extensive and diverse of the two, and it is generally regarded as the best place in the world to see living marine stromatolites.
Is the Hamelin Pool boardwalk open?
It has been closed since 2021, when Cyclone Seroja damaged it, and the microbial mats cannot be walked on directly. A rebuild reported at around $4.6 million has been described as scheduled to begin in 2026, but no reopening date should be assumed. Check with the Western Australian parks authority before travelling; most travel articles still describe the boardwalk as open.
Can you still see the stromatolites without the boardwalk?
Yes, from the shoreline, about 750 metres from the car park along compacted gravel. Go at very low tide, when the colonies stand clear of the water, and bring binoculars or a telephoto lens. It is a less immersive view than the boardwalk offered, but the colonies are visible.
How old are the Hamelin Pool stromatolites?
Two different ages are relevant. The stromatolite lineage as a form of life goes back roughly 3.5 billion years, and the structures represent life on Earth between about 3.5 billion and 700 million years ago. The individual columns at Hamelin Pool are far younger: a metre-high column may represent several thousand years of growth.
What is Shell Beach at Shark Bay?
A beach made not of sand but of coquina — billions of tiny shells from a single cockle species that thrives in the hypersaline water where its predators cannot. The shells are packed metres deep, and further inland they have been quarried in solid blocks and used as building stone.