Blue Lake at St Bathans in Central Otago was formed through gold mining activity from the 1860s till 1934. Originally the lake was a 120m high hill.. Kildare Hill.. which I’ve read was demolished via hydraulic sluicing in about 10 years. By using a hydraulic elevator the site of the now-gone hill became an ever-growing pit until work stopped in 1934 because the town itself was in danger of being undermined. Once the work stopped the pit filled with water. Depending on what source I read the pit was 60 / 68 / 70 metres deep.
The story of the geology of the site, and why the gold is even found here, is pretty interesting:
Blue Lake by Kate Pedley (University of Canterbury)
St Bathans – Blue Lake and how the gold got there (Department of Geology, University of Otago)
Text and photos by Liz; Exploring Colour (2022)
Exploring Colour 
Brings back memories. We detoured up to St Bathans one when we rode the Rail Trail
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Lovely place to visit in nice weather, hope you had a chance to look around a bit. We’d like to go back and stay for a few nights.
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Wow. Looks so unusual. Hopefully it will continue to recover.
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It’s a place with a special feeling about it these days. Which is strange when it’s been through so much upheaval!
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