The Waikato Regional Council started monitoring 50 sites around the district in 2002, calculating a Macroinvertebrate Community Index score (MCI) which assesses the health of a waterway based on the types of macro-invertebrates found and their sensitivity to organic enrichment.
The council recently scored the Careys' stretch of the Marokopa at a level considered 'excellent' and just short of the highest possible rating.
Efforts to improve water quality have continued through the conversion of one of the farms to dairying nearly a decade ago. The Careys also decided to go organic at the same time, eliminating the use of antibiotics and pesticides in their farming practices; they are shareholders in an organic retail business in Hamilton.
"When we got into dairy we decided to go all out and fence off all the river, before it was compulsory," Carey says. They fenced all the farm's wetlands and river frontage — 23 km of it — and started on a comprehensive riparian planting programme which has seen around 10,000 trees and other plants go into the ground.
"Our whole idea was to keep the river as perfect as it could possibly be," Carey says. "The Marokopa is a mudstone river, not a lovely stony river, so a lot of the time it looks murky, but you can tell the health of the river by the aquatic life in it."
The Careys were also one of the first to put in an effluent separator, which sees all solids removed and the liquid portion stored in a large capture pond which can hold 4.5 million litres — about six months' worth. This natural goodness can then returned to the environment safely through a mobile irrigation system, which can cover 90 hectares at a time.
"It's a very good fertiliser. We're very strict about keeping it away from the margins of the waterways. Even though we've got a lot of vegetation around them, we still don't go closer than 25 or 30 metres from the water."
This is in stark contrast to Carey's memories of farming practices when he was growing up on a farm in Arapuni, south of Tirau in the Waikato.
"When I was 12 or 13 years old, I used to work on a farm nearby that had a beautiful creek going through it. But every day at 9am, it would go from being beautiful clear water to being a stinking brown hole, and you'd know that the farmers were washing the effluent down from the yard after milking. It was the same again at 4pm.
"There's a high cost put on this current generation of farmers to clean it all up, but we're doing extremely well. We're not the minority in having a good clean river — we are actually part of the majority of farmers that are out there doing things for their rivers and their environment."
Carey says when he talks to other farmers in the district about making changes around the farm to improve fresh water quality, he tells them not to wait for regulation and legislation to make it compulsory.
"They need to start straight away – and many of them have. Don't put it off and get massive bills later on. You're also going to get a hell of a lot of good feelings towards it while you're doing it, when you see all your trees and vegetation growing, and see your rivers improving."
For more information on a tool farmers cane use to help plan and cost fencing and planting visit the website here.
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