The imprints were thought to have been exposed by significant flooding in the Maniototo late last year, and it was likely they would not have survived another flood event, Otago Museum natural science assistant curator Kane Fleury said.
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Mr Fleury acted immediately when Mr Johnston sent photos of the footprints to the museum after he found them in early March.
He met Mr Johnston at the site and used an underwater camera, snorkel and mask to examine the markings, which were about 1m under the water.
Seven clear footprints were found, each about 30cm by 30cm, and an action, preservation and excavation plan for the footprints was immediately prepared.