A Golden Bay freshwater salmon farm was almost wiped out by a wave of mud and logs during heavy rain on Sunday.
Anatoki Salmon lost its main farm buildings and most of its salmon stock.
Marketing manager Dan Van Dereyk said he and owners, Gerda and Jan Dissel, tried in vainto unblock the salmon pool outlets.
But the farm, which is beside the Anatoki River, was overwhelmed by the debris.
Mr Van Dereyk said the mudslide caused about $500,000 worth of damage. He believes about 5000 salmon are left for this season.