The West Coast is today celebrating meeting water quality standards for Lake Brunner five years ahead of schedule.
Lake Brunner, about 30km southeast of Greymouth, is the largest lake in the northwest South Island. It covers an area of 40 sq/km.
In January this year, water monitoring data showed the lake met the quality standard set in the West Coast regional council's land and water plan.
Westland Milk Products chairman Matt O'Regan said it was decided as far back as the early 1990s that action was needed due to the lake's deteriorating quality.
Since then the council had been working with farmers and the community to improve it by focusing on changes to farming rules and regulations.
"Farmers all had to get new resource consents. The ones they did have were removed; they applied for new ones and had to change their practices and spend a lot of money on effluent systems."
Other changes included the types of fertilisers used on the farm, and how they were applied. Farmers also had to fence off waterways, and plant along riparian strips.
Mr O'Regan said the new system was fully put in place in the past couple of years and the water quality improved in record time.
"It had until 2020 to run before they expected the lake to be at a level that was acceptable, but within two years of this being implemented the water testing has shown that the lake is now at a level that is acceptable."
He said most farms had to upgrade their effluent systems, which could be very expensive.
"In some cases farmers have had to spend in excess of $200,000 just to continue the right to farm the land that some of them have farmed for years and years through their family.
"But it is recognised that if you're going to farm today you're have to be environmentally sustainable as well as financially sustainable, so those are the sorts of things that farmers have done."