Waikato Federated Farmers is warning that there would be a massive impact on the local economy if computer-modelling to improve water quality in the region was followed through.
The modelling has been produced to look at the impacts of implementing changes, such as land-use and in particular moving away from dairying.
It is estimated it would cost anywhere between $1 and nearly $8 billion over a 25-year period to clean up the Waikato and Waipa rivers and their tributaries.
It is based on scenarios ranging from making the rivers suitable for swimming, fishing and healthy biodiversity, to no further water quality decline, but with some improvements, or just holding-the-line with no further degradation.
Scenario one would require a 22 percent reduction in dairying.
Waikato Federated Farmers president Chris Lewis said it would halve the region's gross domestic product.
"...in food processing, agricultural support industries, retail trade, manufacturing, agriculture and other professional services, so this is something which will be concerning not just for farmers, but the whole urban population, the whole community and it could lead to a massive amount of job losses and depopulation of the region I think."
He said it was always easy to point the blame at the farming sector.
"Farmers have spent hundreds of millions of dollars in Waikato on improving their situations. Most farmers tell me all they want is an even playing field.
"What is good for the rural community has to be the same rules for the urban community and if that happened, I think the urban population may not be very happy because some of the district councils will have to spend hundreds of millions of dollars to get to the same level of rules that farmers have."
He said improvements could still be made to the environmental impact of farming.
"I look at my own farm and I have spent about $300,000 but I still see a few things where I can improve on.
"We have that in our plans when the pay-out comes right to keep improving and with new technologies and hopefully new scientific breakthroughs, these issues will get a lot easier."