A high-tech sonar device and eight days of hard work in wild weather has solved the mystery of Australia's deepest lake.

The exact depth of Lake St Clair in Tasmania's picturesque Central Highlands has previously been unknown, with guesses ranging from 160 to 215 metres.

Mapping from a CSIRO team using a remote-operated vessel dubbed the "otter" has officially confirmed its maximum depth - a plunge of 163m.

The figure is well beyond any other lake in Australia and is around twice as deep as Bass Strait, which reaches approximately 85m.

"Lake St Clair is absolutely Australia's deepest lake, with the next deepest lake being less than 100m deep," CSIRO hydrographic surveyor Augustin Deplante said.

"We found Lake St Clair's deepest point is close to the western shore on the bend in the la

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