ORC compliance manager Martin King said the Otago Fish and Game Council reported the incidents to the regional council for investigation over the past couple of weeks.
A duck shooter, who did not want to be identified, told the Otago Daily Times he had seen dairy cows grazing in large ponds near the Taieri River at Patearoa on three consecutive weekends in June.
Concerns were raised about the possibility of effluent from the cows being discharged into the waterway, and of surrounding land being damaged by the stock.
Mr King said the council was investigating and staff members were exploring the area in question.
Such complaints were often difficult to resolve, as by the time council staff investigated certain areas, cows had been moved to different ground.
"It is not the first time we have had this reported to us and each time we investigated it, the cows have been outside of the [waterway] zone.
"Under our rules farmers can put stock in such areas as long as it doesn't cause pugging, damage river banks, or create effluent in the water," Mr King said.
