New information has been released about the location of some of Northland's most coveted and controversial resources.

The Ministry for Primary Industries has released a report citing where, it believed, the largest deposits of swamp kauri could be found.

The report said the biggest amounts could be found in Mangawhai, Hikurangi, Awanui, Ruakaka and pockets along the coast from Kaihu to Pouto.

The National Institute of Water and Atmospheric Research (Niwa) used ecological, geological and historical tools to map the distribution and remaining volume of swamp kauri across Northland.

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The report said approximately 50 per cent to 70 per cent of swamp kauri was still in the ground, but some of this would not be approved to be extracted.

Northland Environmental Protection Society chairwoman Fiona Furrell said the locations identified in the MPI report were unlikely to surprise those wanting to extract the timber. She believed they already knew where to look.

However, Forest and Bird's Northland conservation advocate, Dean Baigent-Mercer, said he was concerned about the MPI using public money to show companies where more precious swamp kauri might be located.

Mr Baigent-Mercer said the milling of swamp kauri had dramatically increased in the past five years.

"It's been a crazy gold rush," he said.

However, he said it would be difficult to pin down the number of swamp kauri left, as so much milling had been unmonitored, leaving it unclear how much timber had been exported.

He said the report showed the MPI was uncertain about the trading of swamp kauri timber in an environment of poor monitoring and regulation enforcement.

"This is what happens with a lack of enforcement," he said.

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Ms Furrell said the milling of swamp kauri had caused major problems for Northland wetlands, as areas were drained to allow easier access and extraction.