Dairy NZ wants Sir Tim Smit to come to New Zealand for a dip in a river after the prominent UK environmental entrepreneur publicly likened the country to "a beautiful person with cancer".

The industry body has hit back at remarks the English businessman made at a London conference this week.

But other groups have backed Sir Tim's blaming of dairying for tainting New Zealand's clean, green tourism brand.

And Environment Minister David Parker has also acknowledged the problem.

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"You know, what is the brand New Zealand guys? You know, it's the oldest advertising thing for a place in the whole of the world — Pure New Zealand," Sir Tim told the Country Land and Business Association's Redefining Farming conference at Westminster.

"It's so pure that the people of Christchurch won't even swim in the River Avon.

"It is like a beautiful person with cancer. Why? Because there was no strategy. The only strategy was to satisfy consumers in China with dairy product, which is ironic for a lactose intolerant people."

Sir Tim, noted for co-founding The Eden Project: an eco-tourism initiative and educational charity that opened in Cornwall in 2000, and which has since inspired a similar project based in Christchurch's Avonside, said increased high rainfall events expected under climate change would worsen pollution of waterways with nitrate loads.

DairyNZ strategy leader Bruce Thorrold said the industry group was "extremely disappointed" at the comments.

"We acknowledge that not all of our waterways are pristine but compared to the rest of the world, New Zealand's waterways are in good condition, and our farmers and communities are working hard to be even better," Thorrold said.

"And dairy is just one sector that has had an important role to play. The Avon River, which Sir Tim references, is the river that flows through Christchurch City and isn't anywhere near dairy farms."

New Zealand was "still very much a 'beautiful person'," Thorrold said, "and proud of it".

He noted the country was among the top 10 per cent of countries in the world for environmental performance and argued Sir Tim's comments didn't reflect that many rural waterways and lakes were improving.

"Dairy farmers and the Government have recently invested millions of dollars into innovation, research and science to continue to be world-leading in environmental solutions on farm."

"We invite Tim to revisit our beautiful country, and his facts, so he can see first-hand the state of our rivers and lakes, and perhaps even take a dip."

But other groups have backed Sir Tim's comments, which come after New Zealand's freshwater issues have been highlighted in major international outlets including The Wall Street Journal, The Guardian, The Economist, The New York Times and Al Jazeera.

"What's happening is the international community is starting to cotton on that our clean green image is a facade," New Zealand Fish and Game Council chief executive Martin Taylor said.

"Now we've got one of the world's leading environmentalists saying it for what it is: that for the last decade, we've put environmental concerns second and development and dairying first, and the outcome is you have degradation of our waterways."

Greenpeace campaigner Gen Toop said Sir Tim's comment's were "sadly, absolutely right".

"The tourism industry has already backed calls for a reduction in cow numbers and a removal of state funding for big irrigation."

David Parker said today: "We agree New Zealand's got a real issue with water quality - we campaigned on it, and we are going to do something about it."

A recent Government report found dismal trends for two key nutrients, nitrogen and phosphorus, that increase the risk of river-choking algal blooms and are often linked to agricultural intensification.

It showed how nitrogen levels were worsening at more than half (55 per cent) of monitored river sites, compared with the 28 per cent of sites that were improving.

Phosphorus levels, meanwhile, were improving at 42 per cent of sites — but getting worse at a quarter.

Other figures in the report showed nitrogen leaching from agricultural soils was estimated to have increased 29 per cent from 1990 to 2012.