TASMANIA: World-first mapping reveals the true depth of Australia’s deepest lake

Lake St. Clair in Tasmania: Australia’s deepest lake has now been mapped – Image: Wikimedia Commons/COLJONES

A high-tech mapping team from CSIRO, Australia’s national science agency, has produced an incredible new view of one of the most iconic natural features in Tasmania and Australia’s deepest lake, Lake St Clair in Tasmania’s central highlands.

Using advanced multibeam sonar and Light Detection and Ranging (LIDAR) technologies, the team has presented to the public the first high-resolution 3D map of the lakebed and shoreline, uncovering dramatic underwater cliffs, deep ravines and towering rock formations.

Lake St Clair was carved from the surrounding bedrock by ancient glaciers and is internationally known for its wild beauty as part of the UNESCO World Heritage Cradle Mountain-Lake St Clair National Park. However, the maximum depth of the lake has never definitively been confirmed, though past reports estimate it between 160-215 metres.

Topographical map of central Tasmania overlaid with CSIRO’s new high resolution mapping of Lake St Clair, Australia’s deepest lake – Image: CSIRO

Deeper than Bass Strait

CSIRO’s mapping has now officially confirmed its maximum depth, with the lake plunging to 163 metres. This is far deeper than any other lake in Australia and deeper even than Bass Strait, which has a maximum depth of approximately 85 metres.

CSIRO hydrographic surveyor, Augustin Déplante, said the mapping offers a stunning new view of the lake and solves the mystery 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 meters deep,” Mr Déplante said.

“We found Lake St Clair’s deepest point is close to the western shore on the bend in the lake about 4 kilometres north of the visitor centre, but there are several areas where the lake depth reaches 150 metres,” he said.

CSIRO will share the 3D dataset with various stakeholders to support increased understanding of the lake’s underwater habitats and how it was formed. The data will also assist safe navigation on the lake and future research, including the use of the lake for testing autonomous underwater vehicles.

The team battled wild weather to systematically map the lake over 8 days using advanced, high-resolution multibeam echosounders, a type of sonar which use pulses of sound to measure the water depth.

Lake St Clair, Tasmania, viewed from south, with colours representing water depth: red 0m to purple 163m – Image: CSRO

No Loch Monster

“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.

The project was led by CSIRO’s Engineering and Technology Program in Hobart, with support from the Autonomous Sensors Future Science Platform. These programs deliver a wide range of expertise and advanced technologies to support Australia’s marine, freshwater and terrestrial research, including in remote and complex environments. (NAN/CSIRO 15-11-25)

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