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Engineers and geologists are inspecting the newly-formed lake in Mt Aspiring National Park, as water continues to lap over the dam caused by a landslip.
Department of Conservation spokesman John Gordon says since water started over-spilling last night, the flow of water has been steadily increasing.
There is concern millions of cubic metres of water will crash down the valley if the dam bursts however Mr Gordon says the dam is not yet showing any sign of instability.
"The concern all the time has been that there's a tremendous weight of water behind the dam and of course, it's not a man made one, it's a natural phenomenon from a landslip, so we can't really ever have any guarantees about it."
DOC is warning telling people to keep well out of the Young Valley in case there's a sudden flood-wave.
- NEWSTALK ZB
