The Otago Regional Council is giving farmers due warning about keeping seepage from silage pits out of waterways.
The council has posted the warning after several cases this year of silage effluent polluting waterways following heavy rain in February and March.
Regional services manager Jeff Donaldson says silage effluent can be a nutrient source for pasture, but it can also be one of the most contaminating farm wastes.
He says it's 40 times stronger than farm dairy effluent, is acidic and contains high levels of nutrients.
Silage stack leakage can cause severe de-oxygenation in waterways, harming fish, plants and other stream organisms.
Dr Donaldson says farmers who have old silage pits close to water should move them.