It has been reported that Horizons Regional Council has shifted to "dispel myths" that the Manawatu River is the dirtiest in the Western world.

But it has been admitted by a freshwater ecologist that it is the unhealthiest river in the nation.

Research by the Cawthron Institute revealed, under a system gauging, oxygen changes in water that the river has by far the maximum reading, since then the condition of the river's struggling ecosystem has become a topic of discussion.

It is said that the river measured 107. Anything more than eight is believed to be indicative of an unhealthy river ecosystem. And a measurement of 0-4 is considered healthy.

The measurement was the highest in a list of 300 rivers and streams across North America, Europe, Australia and New Zealand.

Cawthron Freshwater Ecologist, Roger Young, stated, "There are many millions of streams throughout the world ... if you had 300 people in a room and you measured everyone's blood pressure, it's a big leap to say the person with the highest was the most unhealthy in the Western world".

Mr. Young also said that the Environment Ministry had issued tables on those pointers which put the lower Manawatu in the bottom five out of 77 New Zealand's rivers in each type.

Horizon's Environmental Scientist, Jon Roygard said that the threat it caused to humans differed from day to day.