An environmental trust says iwi are leading the way in cutting the amount of nitrogen seeping into Lake Taupō, but there are fears their efforts to clean up the rohe are in vain.
The Lake Taupō Protection Trust chief executive said iwi have been a driving force in reducing nitrogen levels in the roto.
Graeme Fleming said the majority of nitrogen reduction had come about because of efforts by Ngāti Tūwharetoa and other iwi to lower the amount produced on their lands.
"The majority of the nitrogen reduced actually came from the local iwi lands. Over 65 percent of the nitrogen we reduced came from their lands," he said.
"Partly that was from an economic point of view but also culturally, they wanted to do something about looking after the lake into the future."
Mr Fleming said the iwi did more than just talk about the issue.
"This wasn't just about saying 'I'm talking about protecting it', this was actually action, doing land change to actually help the lake in the future."
However, the Tūwharetoa Māori Trust Board chief executive, Topia Rameka, said the nearby conversion of forestry land into dairy farms may undermine their efforts.
Landcorp is managing the Wairākei Estate dairy farm, which plans to add 33,000 more cows by 2021.
Mr Rameka said that raised fears they could pollute the adjacent waterways, including the Waikato River.
"It is concerning to ourselves and a lot of other iwi that the good work that's taken place in Lake Taupō may come with challenges if there isn't any quick and decisive controls on some of the developments that are taking place in the upper Waikato," he said.
"We've spent a lot of time and effort on the Lake Taupō situation and once those waters flow off the Huka Falls down into the Waikato River system, it's our long term view that those waters are enhanced from Lake Taupō right through to the ocean."
Mr Rameka said an alternative solution should be found.
"The way we approach it should be in a careful, collaborative manner, which needs to involve agribusinesses and large players within the Waikato catchment. Then we need to come up with a solution to realise that there's a bigger prize to be had for our future generations," he said.
In a statement, Landcorp said it had been working on dairy conversions in the Central Plateau since 2004, when it took on a land conversion lease from the land owners, Wairakei Estate.
It said currently, the Central Plateau dairy conversion represents 1.5 percent of all cows in the Waikato region.
"Our operations are required to meet all standards and targets set by regional councils relating to environmental impacts of farming operations. At Wairākei, all current and future conversion work must comply with Waikato Regional Council standards.
"This is constantly monitored by ourselves and council personnel and no concerns have been raised about nitrogen leaching.
"All our dairy farms meet the requirements of the Sustainable Dairying Water Accord and water and nutrient limits managed by regional councils."
Landcorp said it would also identifying new technologies and system changes that would further reduce the environmental footprint of those farms, such as nitrogen inhibiting technologies or fewer cows per hectare of land.
"In all conversions, in any part of the country, Landcorp has been extremely careful to ensure the conversions are environmentally appropriate as well as financially viable. We are driven by our own values as a company to ensure our environmental impact is as minimal as possible."
On Wednesday, it was announced contracts had been signed with land owners to reduce the amount of nitrogen entering Lake Taupō by 170 tonnes a year.