An example of dirty-dairy offending in the 2017-18 year.

They account for just a fraction of the nation's dairy industry, yet the damage they do to the environment and their industry's reputation is profound.

Some were young sharemilkers at the start of their careers, others were old timers with clean records and decades of experience. One was a former Federated Farmers regional leader and prospective MP. Another was a candidate for an environmental award.

Some have offended before; others made a careless mistake and are genuinely remorseful. Some were companies, some were family trusts.

All have been responsible for actions that have damaged our waterways and added to the accumulating degradation.

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Stuff has been collecting figures on the number of convictions for 'dirty-dairying' offences since 2009/10. These figures represent the most serious offending.

It has resulted in a conviction, or the issuing of an abatement or infringement notice.

The offending has affected streams, rivers and waterways in all corners of the country, but the 20 convictions have involved just a tiny fraction of the 8,000 farm owners and 4,000 sharemilkers.

One case involved that of former chair of Southland Federated Farmers Allan Baird and his companies Vendale Ltd and Benlyon Ltd., where an irrigator gun that was supposed to have automatically turned off, but kept running for 16 hours overnight.

Effluent could be seen more than 2.5km downstream and discoloration was visible days later. Baird withdrew his candidacy to become and MP as a result of the prosecution in June, which saw him and the companies fined $39,600.

Another to be convicted was 71-year-old Warren MacPherson, who farms near Invercargill. He was convicted in December after one of his staff had left an irrigator running for 18 hours without checking on it.

SUPPLIED Fish & Game chief executive Martin Taylor said a small number of dairy farm offenders can have a huge impact on our waterways.

MacPherson, chair of the Makarewa River Guidance Group and in the running for an environmental award, was visibly stressed as he appeared before Judge Dwyer in Invercargill District Court, and fined $41,250.

Fish and Game chief executive Martin Taylor said there may be a small number of offenders but they have a huge impact.

"There is a group of farmers who know what's right and they're doing it, but there's a significant group who know what they need to do but refuse to change old farming practices, or they're so heavily leveraged that they can't invest in changing to become a sustainable dairy farm. Then you've got the small group who know they're doing wrong and don't care. They're a minority, but the impact they have is significant," Taylor said.

. Several cases involved irrigators pouring effluent on paddocks for hours longer than it should have been.

DairyNZ water quality scientist Aslan Wright-Stow said the figures represented the very worst offenders.

"We certainly don't condone the tiny per cent of farmers doing this. I think the compliance message is getting through to the vast majority. There are mistakes, and there are a very few who think 'to hell with it'. Our big aim is to get farmers up to speed with what their responsibilities are," he said.

CONVICTIONS IN 2017/18:

1 - White Waters Ltd and Johannes Vernooij fined $39,250 and $19,625 respectively (prosecuted by Southland Regional Council)

2 - Block 8 Farm Ltd fined $54,000 (prosecuted by Taranaki Regional Council)

3 - John and Alison Vernon fined $45,000 (prosecuted by Taranaki Regional Council)

4 - Warren MacPherson fined $41,250 (prosecuted by Southland Regional Council)

5 - Fernlea Farm Ltd fined $37,500 (prosecuted by Southland Regional Council)

6 - Dunrobin Farm Ltd fined $37,500 (prosecuted by Southland Regional Council)

7 - Travis Langford fined $35,625 (prosecuted by Tasman District Council)

8 - Warren Gill fined $35,000 (prosecuted by Taranaki Regional Council)

9 - Fernraig Farms (2006) Ltd and Bruce McLennan fined $25,300 and $8,400 (prosecuted by Waikato Regional Council)

10 - CJH Dairies Ltd and Aaron Fleming fined $23,700 and $8,900 respectively (prosecuted by Otago Regional Council)

11 - MBL Dairy Ltd and Michaela Coll fined $17,800 and $8,900 respectively (prosecuted by Otago Regional Council)

12 - Acorn Farms Ltd and A&T Dairies Ltd each fined $24,500 (prosecuted by Waikato Regional Council)

13 - No. 2 Annaross Family Trust and Johannus Dekker fined $12,825 and $6,412.50 respectively (prosecuted by Otago Regional Council)

14 - Otakia Pastures Ltd and Caleb Holmes fined $11,900 and $5,900 respectively (prosecuted by Otago Regional Council)

15 - Edward Smith fined $17,812.50 (prosecuted by Waikato Regional Council)

16 - Morrissey Farming Ltd and Christopher Morrissey fined $10,900 and $5,500 respectively (prosecuted by Otago Regional Council)

17 - Grant and Glenis Love fined $16,000 (prosecuted by Otago Regional Council)

18 - Wendon Creek Cattle Co. Ltd fined $15,000 (prosecuted by Southland Regional Council)

19 - Allan Baird, Vendale Ltd and Benlyon Ltd each fined $13,200 (prosecuted by Southland Regional Council)

20 - Wayne Carpenter sentenced to 150 hours community work (prosecuted by Southland Regional Council)