Radio New Zealand - Te Reo Irirangi o Aotearoa

Fishermen and tourism operators on the Manawatu River say they're sick of it being used as a drain for industrial waste and are demanding tougher penalties for polluters.

A report has found that by one measure of oxygen content, which indicates pollution, the Manawatu is the worst of 300 rivers and streams tested in Europe, North America, Australia and New Zealand.

Its dissolved oxygen level was found to be 100, when zero to four is considered healthy, the study by Nelson's Cawthron Institute found.

Fishing enthusiast Doug Stevens says some parts of the Manawatu River are a disgrace, especially in the summer.

A tour guide, Andrew Watt, says he's regularly forced to change where he takes tourists because he can't always find the pristine water they expect to see. However he acknowledges farmers are improving their practices.

The report was comissioned by the Manawatu-Wanganui regional council, whose chair Garrick Murfitt says the river is no more polluted than many others.

Twenty years ago, he admits, raw sewage and offal were going into it, but he says it's getting better all the time "and the tests show that."

The council's regulations and planning manager, Greg Carlyon, also says the research is misleading. The river has high levels of nitrogen and phosphorus, he says, but is nowhere near as polluted as many others.