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The Waipori township, west of Dunedin, was flooded in 1924, erasing a once-bustling gold-mining town.
Local amateur historian David Still said the lake was at its lowest since the 1970s - and in his living memory.
Two sizeable items, which appear to be the remains of a gold-mining dredge and farming equipment, are now visible.
Mr Still had never seen either of the items until contacted by the Otago Daily Times and described it as "fantastic news".
"The lake [level] has always fluctuated up and down throughout the year because of electricity demand and if maintenance needs to be done.
"But I have not seen the lake this low since the 1970s."
Mr Still described it as an important part of the country's history and said it should be preserved.
Otago Southland Heritage New Zealand Area Manager Denise Anderson agreed.
While she was aware water levels were "significantly low", she was unaware items had been exposed, until contacted by the ODT.
He identified two of the bigger items as "wagon wheels and a plough".
Mrs Anderson said it was not possible to confirm the age of the items from photographs but guessed they could be pre-1900.
She warned would-be prospectors and reminded looters that it was "unlawful" to disturb an archaeological site as there could be "evidence relating to the history of New Zealand".
"Archaeological sites are irreplaceable parts of our heritage."
Mr Still, who has studied the site for 50-odd years and is part of a heritage group trying to protect the area, also planned to visit in the coming days.
"The preservation of its history is important and making that information available for the public.
"We already have a lot [of relics] in storage, including a photo collection of over 300 photos.
He gave an insight into the items.
The concrete structure visible was part of a water tower and was the killing shed/meat store.
He first visited the site 50-odd years ago and is something of an expert on local history.
"The fact that this [the lake] has gone down and exposed all these paths is unusual."
The town shot up quickly when it was formed on December 17, 1861.
Records show some men heading overland from Dunedin to join the gold rush at Gabriels Gully, near Lawrence, found gold in Lammerlaw Creek.
In less than a week, about 400 gold miners were working the banks of the creek and its tributaries.
He described it as timely - they plan to meet in the coming weeks to talk about fundraising.
The ultimate aim was to build a museum to house all the artefacts, including any new ones.
Trustpower did not respond to questions about how long the levels would remain low, or whether it was a permanent fixture.
Trustpower reduced the level by 2.1 metres following a safety review which found the dam walls could fail in an earthquake.