Otago Regional Council has called farm owners and managers in the Tokomairiro area of South Otago to a forum on Thursday to discuss a serious decline in water quality in the catchment.
A state of the environment study of water quality and ecosystem health has revealed a marked deterioration in water quality in recent years.
Monitoring carried out on the Tokomairiro River between 2006 and 2011 reduced its classification from good to fair, making it one of the most polluted rivers in Otago.
The council's environmental information and science director, John Threlfall, says the catchment now exceeds the guidelines for bacteria, sediments, and nutrients.
Dairy, sheep and pig farming, the type of drainage systems and the type of land in the area are all factors in the pollution, he says.
Otago Regional Council says the forum in Milton is a chance for farmers to learn what they need to do to be compliant with the Otago Water Plan.