For most of the day, the Indian Ocean conceals one of Australia’s largest and strangest marine landscapes.

Then the tide falls.

A reef the size of a city seems to rise from the water. Rapids tear through narrow channels. Waterfalls spill from its edges. Turtles, sharks and sea snakes scramble toward deeper water before the exposed platform dries beneath the Kimberley sun.

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Australia’s Montgomery Reef Emerges From the Ocean

Montgomery Reef, known to its Dambimangari traditional owners as Yowjab, lies off the remote northwestern coast of Western Australia. It covers roughly 100,000 acres and becomes visible for only a few hours around low tide, according to Smithsonian Magazine.

The reef does not actually rise. Water levels can fall by as much as 33 feet, exposing broad terraces, shallow lagoons and rocky islands. Satellite images published by NASA Earth Observatory show how the sprawling formation shifts from an almost invisible underwater shelf into a sharply defined landscape.

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Waterfalls Trap Wildlife in a Race Against the Tide

As the sea drains, water trapped behind ridges of algae pours toward deeper channels. The current can reach about two meters per second during powerful spring tides, the Western Australian Department of Primary Industries and Regional Development reports.

Fish, turtles, snakes and blacktip reef sharks can be swept over the reef’s edges. Some animals become stranded until the ocean returns.

Around 300 square kilometers may stand exposed at low tide, while reef egrets patrol newly opened pools for prey, according to Oceanographic Magazine.

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An Ancient Reef Built by Algae

Montgomery Reef differs from most coral structures. Beneath its marine life sits an ancient tableland of sandstone and dolomite. Coralline algae called rhodoliths form mobile ridges that trap water and help create the reef’s lagoons.

Hard and soft corals grow mainly around pools and channels. They endure direct sunlight, wind, dramatic temperature changes and hours of exposure to open air. The Pew Charitable Trusts describes Kimberley corals as among the world’s most resilient, with roughly 400 species recorded across the region.

Even the Toughest Corals Face a Limit

Tidal currents may offer some relief from extreme heat. Research from the Australian Institute of Marine Science found that waves and tides can connect reefs with cooler offshore water and rapidly change local temperatures.

But resilience is not immunity. Between 57 and 80 percent of Kimberley corals bleached during the 2016 marine heatwave, with Montgomery Reef among the hardest-hit areas, The Guardian reported.

Each returning tide hides that danger beneath the surface. Within hours, the waterfalls stop, the wildlife disperses and Australia’s ghost reef disappears into open ocean once more.