Aspiring Environmental director Chris Arbuckle, who worked as a senior adviser for Government on freshwater management, said he was ''disappointed'' by critics of the proposed amendments and said it showed they had ''missed the point'' of the policy statement.
Mr Arbuckle contacted Southern Rural Life following criticism of the proposed amendments by freshwater scientists in last fortnight's paper.
The proposed amendments include the creation of a national framework for freshwater management, setting bottom lines for maintaining ecosystems and human health, the requirement for councils to account for all water takes and contaminant discharges, and recognition of the value of freshwater to iwi.
Some said the proposed limits were not strong enough and would allow environmental decline of freshwater to continue.
However, Mr Arbuckle said policy was only effective if those who had to implement it, understood it and were able to work within the limits set.
While some of the policy allowed for misinterpretation, ''the core of the National Policy Statement for Freshwater Management is about maintenance and improvement''.
The policy gave communities the ability to control their waterways as they saw fit, he said.
''Take Waituna, in Southland, for example. If you want that to turn back to a stage of excellent water quality, you are going to have to remove all the dairying,'' he said.
The policy statement allowed the community to make the decision to do that if that was wanted, Mr Arbuckle said.
However, communities and land users had to be able to work within the limits and under-stand what they meant to day-to-day activities, he said.
''There are people within the bell-shaped curve of behaviour that won't change, but the majority of people will change behaviour if they are given the tools to do so,'' he said.