Only a year ago the Environment Minister was saying that aiming for swimmable rivers was "impractical".
So what changed to make it practical?
Over the summer there's been a tipping point in public opinion.
Thanks to efforts by many environmental groups a majority of New Zealanders came to understand that dirty rivers were a serious problem - and industrial dairying is a major culprit.
How do you make the public an election promise about freshwater without actually doing anything to clean up the rivers? Change the standards.
It almost reads like a script from the British political satire The Thick of it.
You can just imagine the profane PM's chief of staff Malcolm Tucker saying to his Environment Minister: "I don't care for that fact - get me another one."
The fact in question was an inconvenient baseline for swimmable rivers.
Until Thursday morning the officially-accepted figure for the percentage of NZ's monitored rivers that were swimmable - according to NIWA - stood at 38 per cent.
In a twinkling of the eye, with barely a ruffle of his magical robes, Smith has nearly doubled that figure to 72 per cent.
How did he manage it? Simple. By changing the standards. Hey presto the new freshwater guidelines were born.
Under the new regime a river is deemed swimmable even if it has an e-coli reading of 540 per 100 millilitres.
That level of bacteria from faecal matter means a one in 20 chance of contracting campylobacter if you go swimming there.
As prominent freshwater scientist Mike Joy points out that's like giving a restaurant a hygiene certificate even though you know that one in every 20 customers will get sick.
That is not clean, or swimmable by anyone's standards.
Rivers that our Ministry of Health used to call "poor and fair" - because of the levels of e-coli - are now considered "excellent" quality when you put on the Government's new standard goggles.
This cynical sleight of hand means New Zealand kids are even more likely to become ill because their parents will think they are swimming in a clean river, when they're not.
Smith has made much of the $2 billion dollar cost of cleaning up thousands of kilometres of waterways by building fences to keep the cows out.
This ignores one of the central problems of river pollution in NZ - too much cow urine from too many cows. It falls straight onto the paddock, and when there's too much of it it goes through the soil and into waterways. No amount of fencing can stop that.
When it comes to the nitrogen pollution issue the Government hasn't even bothered to try and make it look better on paper.
The current bottom line for nitrates is what's called the nitrate toxicity level.
That's 6.9 mg/L - the amount at which nitrates start directly killing fish in a laboratory environment. Way earlier is the crucial point when algal blooms start appearing and sucking oxygen out of the river.
We can only hope the Minister for Magic has another trick up his sleeve that can make fish live when there's no oxygen in the river, because at the moment already 75 per cent of our freshwater fish are considered threatened with extinction. The algal blooms choking up our waterways are a national disgrace.
The Government has once again put Industrial dairying ahead of our rivers and for that matter the safety of our children.
Actions speak louder than words.
These new guidelines appear to many observers as a modesty screen to shield industrial dairying so it can keep on polluting.
The Government is quietly forging ahead with incentives to encourage more industrial dairy conversions, despite what it's doing to our rivers.
Hovering like a death eater above our environment - a $400m fund earmarked to subsidise irrigation schemes which will encourage more industrial dairying.
Our own Commissioner for the Environment has made it clear, more industrial dairying will mean more pollution.
It will, by definition add more nitrogen rich urine and bacteria packed poos to our rivers and lakes. We need less cows, not more.
Greenpeace is urging the Government and the industry to ditch plans to build think-big irrigation schemes and urgently reduce the national dairy herd.
Then we need to take concrete action to diversify our farming sector away from industrial dairying and implement other methods of farming which improve our ecosystems and protect our precious rivers.
This swimmable rivers announcement is election candy. The sort you might get on the train to Hogwarts. Bertie Bott's every-flavour beans. The ones that taste like sick.
• Gen Toop is a Sustainable Agriculture Campaigner for Greenpeace
