The effluent irrigator was set up and Mr Hart told it would be "fine" left where it was.
However, on February 6, the relief milker found the irrigator arm broken, disconnected the hose, placing it on the ground. That allowed effluent to flow onto land about 4m from Ashby's Rd drain along the southern boundary of the farm. It flows into the Tauherenikau Seepage Drain - which feeds into Lake Wairarapa.
More than 90,000 litres of effluent was illegally discharged as Mr Hart continued milking the 320 cows twice daily until February 11; the day after Donald returned from holiday and arranged for an engineer to repair the irrigator arm, Mr Gilbert said.
An enforcement officer noticed the disconnected hose with a large volume of fresh effluent ponded around the outlet and flowing through the paddock and nearby trees and bushes and into the drain.
With eight milkings while the hose was disconnected, it was estimated between 90,240 and 135,360 litres of effluent was discharged illegally.
Donald used a portable pump to remove as much from the drain as he could.
Subsequent water quality samples taken in the tributary showed increased faecal coliforms, ammoniacal nitrogen, and phosphorous below the point of the discharge. That rendered water downstream of the farm unsuitable for stock consumption.
Lake Wairarapa had been left damaged by years of dairy farming, Mr Gilbert said.
"It's clear it has been degraded over the years by the dairy industry."
Although Donald accepted full responsibility, he still needed to be held accountable, Mr Gilbert said.
"Further milkings occurred ... this was high on the scale of deliberateness."
He noted the farm had two previous infringements, albeit prior to 2005 when the farm underwent infrastructure improvements.
Mr Gilbert said an appropriate fine would be between $70,000 and $80,000.
He opposed a discharge without conviction submitted by defence lawyer Louise Elder.
Donald plans to develop infrastructure to contain effluent in storage tanks.
Ms Elder said her client was deeply regretful about the incident and had done everything to resolve the problem at the earliest possible time.
A conviction would affect her client travelling overseas as a cattle judge.
It was not a deliberate act, she said.
"You can imagine how devastated and humiliated this is to have happened on his farm ... he is a responsible farmer. It's incredibly embarrassing for him."
Plans were under way for improvements on the farm involving effluent storage systems, which the regional council would soon require all dairy farmers to do.
"Yes, it is something he has to do but he wants to do it straight away. He wants to do this sooner rather than later."
Judge Thompson said while it was an "unhappy incident" dairy farmers had to manage dairy effluent appropriately.
"I have no doubt Mr Donald has learnt a hard and difficult lesson ... the message to the dairy industry is that dairy effluent has to be managed."
Meanwhile, Green Party agricultural spokesman Steffan Browning said while most farmers worked hard to comply with environment rules there were always some who "cut corners".
Hefty fines like Donald had to pay were a deterrent but stronger rules were needed as a Parliamentary Commissioner's report highlighted best practice wouldn't halt the decline in water quality in some regions, he said.
"If we want to protect our rivers and lakes we need strong rules as well as good enforcement ... without strong rules we will see more signs warning people that it's not safe to swim and end up with more rivers that are little more than industrial drains."
