The Manawatu-Whanganui Regional Council says it is not only farming that has contaminated the Manawatu River.
Scientists involved in research on pollution in the river are presenting their findings to an independent hearing panel which is in the final stages of considering the regional council's land and water plan.
The research, commissioned by the council, was carried out by Nelson's Cawthron Institute.
It showed the Manawatu River was most polluted out of a group of 300 rivers and streams in North America, Europe, Australia and New Zealand and led to claims that the river was one of the the world's most polluted.
Scientist Roger Young says the research was designed to give the regional council an indication of the river's health, which he says is very poor. He says it has a very high reading of depleted dissolved oxygen.
The council is also holding a briefing to clear up what it says are myths relating to research on the health of the river.
Dr Young says he has never described the Manawatu River as the worst in the world, and the argument should be about how to try to fix the pollution, not about "who said what".
Head of science at the regional council, Jon Roygard, says treated sewage and discharge from industry are also responsible for the river being classed as one of the most polluted.
However, Dr Roygard says most of the sedimentary pollution in the river is due to erosion from farming, with dairy farms a major source of nutrient contamination.
Dr Barry Biggs, a scientist at the National Institute of Water and Atmospheric Research, says the nutrients create toxic algal blooms that are affecting the fish and other animals in the river.
The chief executive of the council, Michael McCartney, says cleaning up the river for recreational purposes is a priority, but it does not want water use restrictions to affect the region's economy.