This story has been updated because NIWA now says there have been no confirmed sightings of koi carp in Waitomo Caves.
NIWA scientists had to resort to some old-fashioned tools to help prevent unwanted koi carp from reaching Waitomo Caves.
There has been concern koi carp might get into the caves and threaten indigenous species and freshwater habitats.
NIWA scientists were called in to help with the preventative work so the fish could not get into the caves which are a major tourist attraction because of their glow-worms.
NIWA principal scientist for natural hazards and hydrodynamics Graeme Smart spoke to Māni Dunlop.
