Greenpeace was not in breach of the Code of Ethics for its television advertisement which blames cows for dirtying the country's rivers.
The "Save our Rivers" advertisement last year prompted 12 complaints, including one from Dairy NZ, to the Advertising Standards Authority that it was misleading and untruthful.
Dairy NZ said the advertisement portrayed dairy as a major polluter of rivers and waterways.
However, the ASA found that Greenpeace was not in breach, as "parties may express robust opinions as part of the functioning of a democratic society".
The advertisement met the conditions for an advocacy advertisement, as the Greenpeace logo appeared at the end of the advertisement.
"Agricultural pollution is not limited to the dairy farmers. This advertisement provides an undue focus and slant towards dairy as the problem farmer. Anyone seeing this would be easily persuaded to assume that it is dairy farming as the only agricultural polluter of rivers and waterways," the formal complaint said.
Dairy NZ said the content of the ad is unsubstantiated and biased.
Greenpeace weren't surprised by the the decision, however.
The ASA accepted Greenpeace's position that "the impact of industrial dairy farming on water quality is widely documented", Greenpeace's Genevieve Toop said.
"This is the message that the dairy industry has tried, and failed, to stop the public from hearing."
"The advertisement had been placed with a due sense of social responsibility to consumers and society and was not in breach of the Code of Ethics," the ASA chair ruled.