A Navy hydrographic operator readies an Autonomous Underwater Device that will be used at Zealandia.

Navy personnel will be used to map the bottom of a Wellington lake in the hope of finding some historic secrets, such as an historic gold mine shaft.

The Navy's hydrographic experts will work at the Zealandia eco-sanctuary this week to digitally map the bottom of its lower lake reservoir.

It is believed there is an old gold mine shaft, which was used by early miners in the valley, at the bottom of the lake.

MATT DUNCAN/STUFF The lower lake at Zealandia in Wellington. What lies beneath?

By mapping the lake, Zealandia hopes to learn more so the area can be restored, part of its Sanctuary to Sea project.

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Royal New Zealand Navy lieutenant-commander Daniel Wierenga said a team would use side-scan sonar technology to survey the lake floor.

It had been asked to do so by Zealandia, which planned to use a poison to eradicate some unwanted carp in the man-made lake.

If there were indeed old shafts in the water, it was possible some of the fish were in there and would not be exposed to the poison.

"There are some suggestions there may have been some mine shafts where that lake was created," Wierenga said.

"So they're a little concerned if the mine shafts are there, they may not be able to get the poison into all of the fish correctly."

The operation should take about two hours.