CSIRO Confirms the True Depth of Lake St Clair Using High Resolution Multibeam Mapping

Australia’s deepest lake has finally been measured with scientific certainty. A dedicated CSIRO survey campaign has confirmed that Lake St Clair in Tasmania reaches a maximum depth of 163 metres. This makes it the deepest lake in Australia by a significant margin and deeper than Bass Strait, which reaches approximately 85 metres at its deepest point.

The new depth was determined through a complete, high resolution underwater mapping project that used advanced multibeam echosounders supplied and supported in Australia by Seismic Asia Pacific.

A Glacial Landscape Measured With Modern Technology

Lake St Clair was formed when ancient glaciers carved a deep basin out of the surrounding bedrock. While the lake has been the subject of scientific curiosity for decades, its exact depth had never been definitively confirmed. Previous estimates varied widely, and attempts to measure the full underwater landscape were limited by weather, equipment, and access to precise technology.

CSIRO set out to close this knowledge gap by conducting a comprehensive bathymetric survey of the entire lake. Over eight days, their survey team navigated through rapidly changing alpine conditions and strong winds to ensure systematic coverage across all regions of the basin.

High Resolution Multibeam Echosounders Reveal the Full Depth

The breakthrough measurement was achieved using high resolution multibeam echosounders, a class of sonar that emits sound pulses and records their return time to accurately measure depth. These systems create a wide swath of depth points beneath the vessel at very high density, allowing scientists to build a complete digital model of the lakebed.

Multibeam systems of this type are the same class of technology supplied, serviced, and supported by Seismic Asia Pacific throughout Australia and New Zealand. These solutions are widely used for hydrographic surveys, scientific research, port and coastal engineering, environmental monitoring, and offshore industry operations.

For the Lake St Clair survey, CSIRO utilised the NORBIT i80s paired with the SBG Systems Apogee INS, as well as the NORBIT iWBMS Ekinox NT mounted on a Portus Pole. These systems provided the high accuracy and stability required for deep basin mapping.

The accuracy of the equipment, combined with precise inertial navigation and robust onboard processing, made it possible to confirm the true depth of Lake St Clair with confidence.

The survey also deployed the Maritime Robotics Otter USV, an uncrewed surface vessel ideal for shallow water and nearshore coverage, enabling safe and efficient data collection in areas unsuitable for crewed platforms.

The Otter, an uncrewed surface vessel, conducting shallow-water surveys at Lake St Clair to support environmental monitoring and research. Image: CSIRO-Andrew Filisetti.

Survey Challenges in a Remote Alpine Environment

Surveying a deep glacial lake in Tasmania presents unique challenges. The CSIRO team managed:

• strong alpine winds

• rapidly shifting weather across the lake surface

• long survey days in cold conditions

• the need for precise line keeping to ensure full coverage

• deep, steep sided terrain that required careful navigation planning

Despite these challenges, the team achieved full coverage of the basin and delivered a complete, high resolution map of the lake floor.

Why the New Depth Matters

The measurement of 163 metres offers far more than a corrected figure. It improves scientific understanding of:

• the scale of glacial processes in Tasmania

• the formation and evolution of the lake basin

• environmental baselines for long term monitoring

• potential changes in sedimentation and water quality over time

Accurate bathymetry is essential for scientific modelling, environmental conservation, and research planning. This survey provides data that will guide future studies for years to come.

Seismic Asia Pacific Proudly Supports Australian Science

Seismic Asia Pacific continues to work closely with national research organisations, universities, government agencies, and commercial operators to deliver advanced hydrographic and oceanographic technologies across Australia and New Zealand.

From multibeam and single beam sonar to USVs, AUVs, navigation systems, and integrated survey packages, our focus is to provide reliable, high performance tools that enable accurate measurement, mapping, and monitoring of waterways, coastal regions, and offshore environments.

The Lake St Clair project is a strong example of how modern survey technology can unlock new scientific insight and support the long term stewardship of Australias most remarkable landscapes.