Manawatu River tops dirty table

The Manawatu River is the most polluted river of 300 tested in the Western world, according to new research.

The Manawatu tops a new pollution measurement of 300 rivers and streams across North America, Europe, Australia and New Zealand, research by the Cawthron Institute has found.

The waterway is fouled with treated sewage, industrial waste and farm runoff.

Under a system measuring oxygen changes in water, the Manawatu has by far the world's highest reading – almost twice as much as the next worst.

It measured 107 on the scale. Anything over eight is considered an indication of poor ecosystem health. The next most polluted river, sampled downstream from a sewage outfall near Berlin, measured 59.

Roger Young, a freshwater ecologist with the institute, was amazed by the readings from water samples taken at Hopelands, north of Woodville. "To see a count of 100 was just ridiculous," he said.

Tests at Palmerston North were not as high but still indicated poor ecosystem health.

The Manawatu was affected by farm nutrient leaching and treated town sewage, Dr Young said.

"Agricultural use is most of it; nitrogen runoff, mainly."

Other factors were the shallowness and width of the slow-moving river, which exposed it to sunlight that encouraged algal growth.

Massey University ecologist Mike Joy said the research showed the river was "a basket case".

"I've been aware for some time that the river was a pretty sad case, but even I was shocked at this research. It's not just farm nutrients; it's sewage, sediment and river modification issues with stopbanking."

Environment Minister Nick Smith said it was well known that the Manawatu River was in poor shape. It was symptomatic of a national problem with water quality, he said. Cleaning the waterways was a priority.

Palmerston North Mayor Jono Naylor was concerned by the findings.

The council had invested $15 million in the city's wastewater system to improve the quality of sewage discharge into the river, he said.

The Horowhenua District Council admitted in September pumping 5.1 million litres of partially treated sewage into the river over 48 hours in October 2007.

"At the high levels, you virtually have to get some in your mouth and you'll get sick," Dr Joy said.

Public health officials would not comment last night.

Dr Young's research is to be presented to a panel that next week begins hearing submissions on the Horizons Regional Council's One Plan.

- © Fairfax NZ News