Peat fires burning a metre below ground on Department of Conservation land in the Far North will take at least another week to be extinguished.
Firefighters pumped water underground yesterday at the Lake Waikaramu Conservation Area after containing fires above ground that destroyed 62ha of scrub and wetland.
DoC spokesman Glen Coulston said the outbreak, 30km north of Kaitaia, was now at the mopping up stage, but could take more than a week to extinguish fully.
Metal probes are being inserted into the ground to allow water to be forced underground.
The cost of fighting the fire at Kaimaumau has already reached $300,000 to $400,000, according to Far North district principal rural fire officer Lance Johnston.
This includes the $90,000 cost of helicopters with monsoon buckets used when the fire first broke out on adjacent private land last Wednesday and then spread, plus bulldozers to cut access tracks, more than 1000 litres of foam and up to 85 firefighters a day.
The total cost is likely to be paid initially by the Far North District Council and DoC, and then claimed back from the national Rural Firefighting Fund.
Lake Waikaramu is a wetland conservation area, containing rare native species such as black mudfish, green gecko and orchids and is the reason DoC is putting such huge effort into fighting the fires underground.
Subsurface peat fires have sometimes been left to burn themselves out in the past, but there is now a greater awareness of conservation values, says DoC.