Beef and dairy cattle on three farms grazed the unfenced streambank, resulting in fouled banks and stock standing in the stream to graze on river weed and drink the water.
"In all three locations the situation is easily remedied with minimal cost," Ruka said.
Efforts by hapu, the Northland Regional Council, other groups and landowners to fence and replant both banks on a 7km stretch of the Waipao Stream are being undermined by upstream farmers not fencing their banks, Ruka said.
"We commend the farmers who have fenced off more than 90 per cent of the Kauritutahi over this 3km [but] our efforts are undone when farmers upstream do not fence off their properties."
The 1991 Resource Management Act states everyone has a duty to avoid, remedy, or mitigate adverse effects, and photographic evidence gathered during his patrol clearly shows "adverse effects".
Ruka has asked the council to write to and visit the farmers concerned.