Federated Farmers is persisting with efforts to obtain more information from the scientists involved in research which suggests the Manawatu River is one of the most polluted in the world.
The research by the Cawthron Institute in Nelson was issued late last year.
It showed the Manawatu River has the highest reading of depleted dissolved oxygen of 300 rivers and streams in North America, Europe, Australia and New Zealand.
Federated Farmers wants the Institute to name the other 299 rivers on the list.
Spokesperson Lachlan McKenzie says the federation has contacted the institute several times requesting the list and has not had a reply.
He says any claim that a river is one of the most polluted in the world needs to be backed by facts, and Federated Farmers would like to know what the Manawatu River is being compared with.