Some of the milk dumped by farmers in Waikato and Northland has reached waterways.
The closure of the Maui gas pipeline this week prevented processing at 15 Fonterra plants in Northland, Bay of Plenty and Waikato.
Uncollected milk is being collected in effluent ponds so it can be sprayed onto pasture, but Northland Regional Council says milk has entered a stream in the Maungaturoto area.
Spokesperson Tess Dacre says the farmer was intending to put the milk into an effluent pond but the stormwater diverter was set incorrectly and directed it into a stream.
She says it is not known how much milk went into the stream and a decision is yet to be made on whether action will be taken against the farmer.
Four cases reported
There have also been reports of milk in waterways in Waikato, the country's biggest dairying region. Waikato Regional Council says four reported cases are being investigated.
Compliance and education manager Rob Dragten says the small number of reports in a region of 4200 farms shows that the majority of farmers are taking their responsibilities seriously.
He says some of the incidents might be the result of an accident, but the council may take action against anyone found to have deliberately dumped milk in a waterway or disposed of it without adequate care.
Bay of Plenty Regional Council says it has had no reports of milk in waterways.
