Dairy farmers in Collingwood, Golden Bay, hope that milk tankers will reach them by Friday night.
Torrential rain in the past three days has caused widespread flooding and slips in the Nelson and Tasman regions, with Golden Bay the hardest hit.
The tankers were unable on Thursday to collect milk from 43 dairy farms in the Collingwood area, which is isolated by a slip on Bird's Hill on State Highway 60.
Collingwood farmers have so far spilled a day's worth of milk on their paddocks through effluent systems.
Fonterra says they produce 360,000 litres per day and will be paid for any dumped milk.
Federated Farmers Golden Bay dairy chair Sue Brown of Aorere Valley, says the milk dumping is manageable.