More than half of Canterbury's dairy farms are not complying with effluent management rules, a regional council report reveals.
Farmers say they are working to clean up their act, but an environmental group believes their progress is too slow.
The regional council's dairying report for 2008-09 reveals only 368 of the region's 851 dairy farms were fully compliant with effluent regulations.
The council says the figures are consistent with previous years and it is working with the dairy industry to improve compliance.
However, Barry Weeber, of Environment and Conservation Organisations, says he is disappointed compliance has not improved during the past five years.
Mr Weeber believes Fonterra and other milk companies should take action by rejecting milk from farmers who repeatedly breach effluent management regulations.
Though there has been little change in the level of compliance, the council says there has been one positive trend - a reduction in the nitrogen application rate from farmers spreading dairy shed effluent on pasture.
The legal limit is 200kg a hectare a year to reduce the risk of it leaching into ground water. However, in the past year 60% of Canterbury dairy farmers were applying nitrogen at a rate of less than half of that.