A trust set up to reduce the amount of nitrogen in Lake Taupo has reached a key milestone, three years early.

The Lake Taupo Protection Trust was set up in 2007 has been buying land and enforcing land use changes around the catchment ever since.

Minister for the Environment Nick Smith says he is thrilled to announce they are ahead of schedule.

"Today we're marking the fact that that 170 tonne reduction in the amount of nitrates has been achieved in contracts that have been entered into by the trust."