dead fish
Thousands of dead fish have washed up at a river on the Kapiti Coast , leaving local fishermen bemused.

But the Council insists there's nothing fishy about the large-scale stranding.

Newshub spoke to local whitebaiter Swanny, who said he's never seen anything like the amount of Smelt fish that washed up at the Otaka riverbed earlier this week.

He said he's been coming to the river for more than 60 years.

"You catch a lot of Smelt in November in your net. It might be four or five dozen at a time sort of thing, so you just tip them back. But I've never seen nothing like this - this is one out of the books," he said.

Local iwi were the first to alert The Greater Wellington Regional Council to the dead fish,which threatened to disrupt the popular fishing and whitebaiting spot.

Samples from the river were sent to Nelson's Cawthron Institute and their testing found no signs of harmful algae bloom.

Instead, evidence suggests the smelt died from a mass stranding.

The council says there's no danger to public health or the health of the river.

But it's likely to remain a mystery as to why so many fish swam to their deaths.

Swanny says the New Zealand Smelt fish aren't good to eat as they're small and smell like cucumber.

So the remaining dead fish won't be scooped up by locals, who plan to persevere with their rods and whitebaiting nets.