Farmers in Otago say they are only just realising all the effects of tougher new water rules for the region.
A proposed plan change by Otago Regional Council tightens the definition of river quality but leaves farmers to manage agricultural runoff unless it is making streams worse.
Dairy farmers near Dunedin saying they fear the new rules will turn them into accidental criminals.
They were among about 40 farmers and rural representatives who met at Henley on the Taieri Plains on Tuesday to hear from the regional council and industry groups about the changes, called plan change 6A.
Taieri Plains dairy farmer and former regional councillor Colin Scurr says even after two years of debate, he does not know what the new water rules mean.
Mr Scurr says the rules are in force, yet could be changed, and might leave him facing criminal prosecution for relatively minor environmental effects.
Federated Farmers says the changes have far-reaching implications not fully appreciated yet by many farmers.
Otago president Stephen Korteweg says winter grazing will not be possible in places on open soil, and farmers in North Otago will no longer be able to use the flooding irrigation techniques they have for decades.
He says they need to be given more time to digest and then adjust to the changes.
Other farmers at the meeting said the council's reliance on a computer fertiliser budgeting programme, Overseer, as a way to measure nutrient run-off left them vulnerable.
But council land advisor Nicola McGrouther says if farmers resolved all the obvious rule breaches, they would be well on the way to complying.
But Fish and Game Otago says the council has the plan largely right and cannot back down now.
The council will hold public hearings in September.