A former Federated Farmers dairy chair has described trout as the stoat of the waterways, saying the introduced species are a major contributor to declining freshwater quality.
In a speech at the recent annual general meeting before stepping down as the Federated Farmers dairy chair, Lachlan McKenzie said trout are a disastrous species and no better than freshwater stoats.
He says they devour native invertebrates, increasing algal growth, forcing native fish to the brink of extinction.
While he accepts dairy farming does contribute to water quality problems, the effects of trout on flora and fauna in the waterways should also be taken into account.
But some scientists say Mr McKenzie is trying to shift the blame from cows to trout for declining water quality in streams and rivers.
Mike Joy, a senior lecturer of ecology from Massey University, says there is no strong evidence to suggest trout are destroying fresh waterways.
Dr Joy says intensive dairy farming is the key offender, in that the effect of nutrients coming into streams far outweighs the impact of trout.
He says if it was not for trout and the value of the fish to New Zealanders, waterways would be much worse than they are.
Another ecologist, Professor Angus McIntosh from Canterbury University, says Mr McKenzie's suggestion that trout are devouring native invertebrates, increasing algal growth and forcing native fish to the brink of extinction is not true.
Anglers says many low-land waterways are no longer clean enough to catch trout and the fish did not cause that problem - farming and land development did.