CSIRO uses sonar and Lidar to map Australia’s deepest lake
Australia’s deepest lake has just given up its secrets. A high-tech mapping team from CSIRO, Australia’s national science agency, has unveiled an extraordinary new perspective on Lake St Clair, the glacial jewel of Tasmania’s central highlands and one of the country’s most celebrated natural landmarks. By twinning advanced multibeam sonar with cutting-edge Lidar technology, the team has created the first detailed 3D map of the lakebed and shoreline, revealing a dramatic underwater landscape of sheer cliffs, winding ravines and towering rock formations that have remained hidden since the last ice age.
Carved by ancient glaciers and recognized as part of the UNESCO World Heritage Cradle Mountain - Lake St Clair National Park, the lake has long been admired for its wild beauty. Yet its exact maximum depth has never been definitively confirmed, with previous estimates ranging from 160 to 215 metres. CSIRO’s new mapping now officially confirms its deepest point at 163 metres – far deeper than any other lake in Australia and even deeper than Bass Strait, which reaches approximately 85 metres.
CSIRO hydrographic surveyor Augustin Déplante said the mapping offers a stunning new view of the lake and settles the long-standing question of its true depth: “Our mapping confirms that Lake St Clair is absolutely Australia’s deepest lake, with the next deepest lake being less than 100 metres deep.” He added: “We found Lake St Clair’s deepest point is close to the western shore on the bend in the lake about four kilometres north of the visitor centre, but there are several areas where the lake depth reaches 150 metres,” he continued. CSIRO will share the 3D dataset to support research into underwater habitats, geological formation processes, safe navigation and the use of the lake for testing autonomous underwater vehicles.
How it was mapped
The team battled wild weather to systematically map the lake over eight days using high-resolution multibeam echosounders – a type of sonar that uses pulses of sound to measure depth. The project combined data collected by the twin-hulled eight-metre research vessel RV South Cape and a two-metre uncrewed, remotely operated vessel called the Otter, whose compact size enabled detailed mapping in shallower areas inaccessible to larger boats. The Otter also used Lidar to map the shoreline, and this information was integrated with the underwater data to form a single, high-resolution 3D dataset.
“The mapping is highly detailed and can identify objects as small as 50 centimetres in some places. Along the shoreline, it shows the trees that have fallen into the lake and, in deeper areas, has revealed several mysterious features on the lakebed, sparking curiosity about their origins,” Mr Déplante said. “While the data does not confirm the presence of a Lake St Clair ‘Loch Ness’ monster, it does offer a powerful new tool for exploring the lake’s hidden depths. Importantly, the project provided us with the opportunity for cross-disciplinary training for our team and to integrate the latest technologies into our toolbox to enhance the capabilities we offer the research community.”
The project was led by CSIRO’s Engineering and Technology Program in Hobart, with support from the Autonomous Sensors Future Science Platform, both of which deliver advanced technologies for marine, freshwater and terrestrial research in remote and complex environments. The underwater mapping was delivered using Norbit multibeam systems provided by Seismic Asia Pacific.
