Agreements to reduce the amount of nitrogen entering into Lake Taupo have been reached in a bid to improve and maintain water quality.
Contracts with land owners to change the way land is used have been signed which will in time reduce nitrogen leaching by 20 percent or 170 tonnes a year.
Money from an $80 million fund set up to protect the lake has been used to purchase some land and turn dairy farms into forestry and to help farmers find new ways to farm such as reducing stock numbers.
7500 hectares of farmland will be converted to forestry.
Chief Executive of the Lake Taupo Protection Trust, Graeme Fleming, said the contracts would take effect in 2018 to allow time for planting and other land use changes.
"Effectively as of now we have the contracts in place and the public can be secure then about the fact that nitrogen will be reduced."
Mr Fleming said it was a long-term project because nitrogen could take up to 50 years to leach into the lake.
He said it was not a case of forcing people into land use changes but trying to present the best business case they could.
Mr Fleming said with carbon emissions being very topical now it made the trust's case a little easier.
"The business case for land use change to forestry made the case for change very viable."
Mr Fleming said a normal 300 hectare farm produced about three tonnes of nitrogen and to reach the target of 170 tonnes from the Lake Taupo catchment was a real effort but very pleasing to get there.
Ngati Tuwharetoa owns Lake Taupo and was the largest landowner in the catchment.
Chairman of the Tuwharetoa Maori Trust Board, John Bishara, welcomed reaching the milestone of securing agreements to reduce nitrogen by 170 tonnes.
"We all need to stay vigilant to ensure protection of Lake Taupo to ensure future generations are able to enjoy it."
The Mayor of Taupo, David Trewavas, said he was very proud of the way the community had pulled together to protect its greatest taonga - Lake Taupo.