A freshwater ecologist says most whitebait species will be extinct by 2050 if they continue to decline at their current rate.
New Zealand freshwater ecologist Mike Joy said four out of the five whitebait species were threatened and three of those species had become threatened in the last 10 years.
He said that if the species kept declining at the same rate they would all be gone by 2050.
"If we don't change what we're doing with intensive farming and that kind of thing, the fish are going to become rarer and rarer until we just don't find them anymore."
It was hard to say how much impact whitebaiting had on the fish, compared to farming and other things, but Dr Joy said fishing was "like a nail in the coffin". The fish were already in trouble and whitebaiting took away the juveniles that should be replacing the populations.
He believed whitebaiting restrictions had needed revisiting for a long time but hadn't been looked at because it would be political suicide for any government.
He'd been advocating to remove the commercial aspect of whitebaiting.
"I think it's fair enough that New Zealanders should have the right to go and catch whitebait within the regulations. What really annoys me is that people do it for a living, so they make money out of destroying something."
He said a good start would be to give whitebait the same protection as trout.
It was good that whitebaiting gave people a chance to get out and appreciate rivers and native fish, but that didn't come from commercial fishing.
Whitebait are made up of banded kokopu, short-jawed kokopu, giant kokopu, koaro and inanga. Dr Joy said all but the banded kokopu were threatened. The short-jawed kokopu was the only whitebait species threatened a decade ago.
According to a recent Department of Conservation review, 74 per cent of the country's native freshwater fish are now listed as threatened.
Dr Joy said that was up on 68 per cent in 2009 and 30 per cent at the first review in 1992.
New Zealand's figures were worse than any other country that kept such measurements. The global average was 35 to 37 per cent threatened.
Dr Joy said native freshwater fish were like miner's canaries measuring the health of rivers.
"When we have those sort of stats, then that's showing just how bad we are in comparison to the rest of the world."
New Zealand had to fix all of its rivers to save its native fish populations.
"What we're doing at the moment is, we're wrecking everything and the West Coast is a really good example."
The West Coast wetlands were being drained and there was a huge increase in the amount of farming, which meant more nutrients and sediment were going into rivers impacting on native fish.
Dr Joy is currently on a lecture tour of the country having won the Charles Fleming Award for his contribution to the sustainable management and protection of New Zealand's freshwater resources.