Hamelin Pool Marine Nature Reserve, Marine nature reserve in Shark Bay, Australia

Hamelin Pool Marine Nature Reserve is a 127,000-hectare protected area in Shark Bay, Western Australia. Its shallow, hypersaline water holds dark, layered stromatolites, from flat mounds to knobbly masses up to 1.5 metres high, built by cyanobacteria at densities of three billion individuals per square metre.

Hamelin Pool was named after Jacques Félix Emmanuel Hamelin, captain of the Naturaliste, who passed the bay in 1801. The marine nature reserve itself was established in 1990. In June 1956 geologists from Denham found the living stromatolite colony, the first known to science; similar colonies were later found in Brazil and Mexico.

The 1884 telegraph station, one of 38 that linked Wyndham in the Kimberleys to Albany, now houses a museum. Its displays cover the station's operation from the 1880s and include an aquarium with stromatolites living in captivity. The old post office, first built in 1886, now serves as the community post office and public phone box.

Visitors can view the stromatolites from a raised boardwalk designed for close observation without disturbing the structures. Swimming and boating are restricted near the formations, so it is important to respect these boundaries when exploring the area.

The boardwalk passes three stromatolite forms: red-capped domes, grey-black and rust-topped, which stopped growing 500 to 1,000 years ago when the water level fell; young tufted mats, black carpets barely a centimetre high; and cauliflower-shaped living columns up to 1.5 metres tall. Growth is about 0.5 millimetres a year, so a metre-high structure is roughly 3,000 years old.