Swim Thru Rottnest

At Rottnest Island off the Western Australian coast, Swim Thru Rotto brings open water swimmers together in protected, glass-calm sea. At the dawn of the southern summer, the event centers on two distinct distances: a 500-metre dash and a 1600-metre course. The morning begins on the shoreline with a traditional Welcome to Country and a Smoking Ceremony, setting a quiet and respectful tone across the sand before anyone steps into the surf. When the races commence, swimmers in the 1600-metre event enter the water in staggered waves departing at three-minute intervals, guided by colour-coded caps that separate each starting group. Once clear of the initial entry, you glide across brilliant white sand where the water is so clear you can watch fish moving across the bottom beneath your stroke.

The course offers a relaxed, unhurried rhythm that highlights the bay's natural shelter. As you swing back toward the beach, spectators line the jetty with cheers echoing across the shallows, welcomed back to the sand by the organizers from The Cottesloe Crabs Winter Swimming Club.

Pleistocene dunes and salt lakes: Rottnest Island's geology

Rottnest Island rests on a foundation of aeolianite limestone, preserved as the remnant ridges of prehistoric Pleistocene sand dunes. Roughly 6,500 years ago, rising post-glacial sea levels cut Rottnest Island off from the Australian mainland, leaving it surrounded by open sea. Standing 19 kilometres off the mouth of the Swan River, the island remains the first piece of land sighted by ships making landfall from the deep Indian Ocean to the west. Twelve inland salt lakes dominate the island's low-lying basins, collectively occupying fully ten percent of its total land area. About two kilometres from Thomson Bay, Lake Baghdad sits as a permanent saline water body ringed by its own quiet, landlocked sand beaches. Even closer to the race start, less than a kilometre away, Government House Lake reveals early bathing heritage where a stone groyne built in the 1930s still features narrow steps carved directly into the limestone cliff.

Bathurst Point to Wadjemup: shipwrecks and navigation lights

The earliest recorded European landing took place on 19 March 1658, when Dutch sailors came ashore in search of survivors from the wrecked Vergulde Draeck. Decades later, in 1696, Dutch explorer Willem de Vlamingh anchored off the coast and named the land 't Eylandt 't Rottenest after mistaking the resident quokkas for giant rats. Treacherous conditions occasionally overwhelmed arriving vessels. In 1899, a violent storm drove the iron barque City of York onto a reef on the north side of the island, while the ship Carlisle Castle was lost nearby on Coventry Reef during the very same tempest. Today, the scattered remains of the City of York—including hull plates, ribs, a deck winch, and a windlass—lie submerged beneath the northern swell about five kilometres away, while its recovered anchor stands preserved on dry land.

In the direct aftermath of that disaster, authorities constructed Bathurst Lighthouse in 1900 at Bathurst Point, throwing a guarding light over the northern entrance to Thomson Bay to ensure approaching waters remained safely marked. Decades later during World War II, coastal defense installations were mounted across the ridges, placing heavy guns at Oliver Hill and Bickley Point that were coordinated from an observation post set beside the Wadjemup light.

The 19.7-kilometre channel: Rottnest's marathon swimming heritage

While Thomson Bay provides gentle, enclosed waters for morning racing, the expanse stretching back to the mainland represents one of the world's storied proving grounds for endurance swimming. Local lore long whispered of island prisoners attempting to swim the wide oceanic gap toward the continent, allegedly using Carnac and Garden Islands as stepping stones across the open swell. That broad passage eventually gave rise to the official Rottnest Channel Swim, covering a grueling 19.7 kilometres from Cottesloe Beach across to the island. The channel was first conquered in modern records on 24 January 1956, when Gerd Von Dincklage-Schulenburg completed the crossing unassisted. In 1969, Lesley Cherriman became the first woman to complete the channel swim, launching from Rottnest's Natural Jetty and pushing through the open ocean toward North Mole. That deep-water heritage imbues every stroke inside Thomson Bay with a distinct connection to Western Australia's open water pioneers.

The Basin and Thomson Bay settlement: island life ashore

Historic limestone cottages line the beachfront, where casual cricket matches and hopscotch on the verandas carry the easy pace of an Australian summer holiday. Swimmers can easily pack goggles and wander along sandy tracks to explore adjacent coves within minutes of leaving the finish arch. Just over the northern rise between Pinky Beach and Longreach Bay lies The Basin, an iconic swimming hollow sheltered between two jagged headlands. There, clear waters shift through vivid shades of green as ocean tides flow over shallow, protecting reefs. Further along the island's rim, surf breaks roll into Bickley Bay and Salmon Bay, while Fish Hook Bay marks the island's western tip, forming a steep 120-metre cove where mutton birds once nested along the wild cliffs. It is a pristine perimeter of limestone and tide, anchored by the calm waters of the bay where the morning's swim began.