Some of the farms hit by flooding late last year in the Tasman district have been inundated again.
Up to 500mm of rain fell during a 24-hour period, flooding farmland in Golden Bay.
Last december, the area received the worst flooding in more than 150 years last December.
Federated Farmers Golden Bay dairy chair, Sue Brown, says more than a dozen farms there are under water.
She says for the second time in six months flooding has ruined much of the pasture on her property, and several of her neighbours' properties.
She will have to buy in winter feed for cows, which will push up costs.
Ms Brown says lack of pasture re-growth since last year's flood had already affected production.
She says farmers were given enough warning to move stock from low-lying areas.