Fisheries officials say natural causes are probably behind the deaths of thousands of fish washed up along the west coast of Northland.
The fish stretch for about 30km along the Ripiro Coast. They were first noticed late last week by people near Dargaville.
The Ministry of Fisheries says early suggestions that they might have been dumped by a fishing boat, have been ruled out.
Northland field operations manger Darren Edwards says that's because the fish are mainly one species - jack mackerel.
He says the most likely explanation is that the little fish were chased to shore by bigger predators.
Mr Edwards says the mackerel were then probably caught in the surf and deposited on the beach.
The ministry will leave it to nature to clean them up.