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Media reports this week say regional councils suspect thousands of tonnes of contaminated waste are being buried on farms every year, with other waste including plastic being burned.
The councils were reported as saying there was little they could do about the practice.
Fish & Game New Zealand chief executive Martin Taylor said a national audit needed to be carried out by the Ministry for the Environment.
"The scale of this threat is significant. We need to know how much discarded spray, insecticide, oil and paint is being quietly buried in farm pits where it will poison the environment for decades to come.
"Not only could toxins flow into streams and rivers already struggling under intensive farming pollution, but it puts aquifers at risk and threatens communities," Taylor said.
He said once the scale of the problem was known, a comprehensive plan was needed to tackle it.
"These dumps must be outlawed. There are schemes and reputable companies which handle such waste safely and efficiently and it should be compulsory to use them."
Environment Canterbury spokesperson Davina McNickel told RNZ said the council was looking into making it easier for farmers to get rid of their rubbish.
She said that at the moment they really didn't have many options.