Manawatu River's health improving, report says

MATHEW GROCOTT
Last updated 16:59 11/04/2014

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The health of the Manawatu River has received a mixed review in a report released today on progress in efforts to clean it up.

The Manawatu River Leaders Accord released its second progress report at Te Manawa this afternoon, marking three years since the accord was signed.

While some key indicators from the report show improvement in the river's health, nutrient, algae and periphyton levels are generally still above the recommended targets in the Horizons Regional Council's One Plan.

River Leaders' Forum independent chair Richard Thompson said improving the state of the Manawatu River was a long-term project, but there were some promising findings in these early stages.

The report's findings include overall improving trends in nutrient levels and levels of bacteria, as set out in an independent science report commissioned by Horizons Regional Council.

However, the level of periphyton in the river has grown over the past five years, an indication water quality is degrading.

"It is difficult to explain why periphyton abundance is increasing when nutrient levels - one of the primary drivers of periphyton abundance - are decreasing," the report says.

Overall the river, when measured against the other 76 monitored rivers in New Zealand, has "relatively poor water quality" on a national scale.

However the state of the river was what could be expected from a waterway in which 80 per cent of the catchment was used in agriculture and just 20 per cent was native bush.

The report says the river is far from being the worst river in the Western World, as was reported by some media in 2007.

"This comment was based on modelling of information collected from a faulty dissolved oxygen sensor that, when used in ecosystem modelling, suggested very high levels of water pollution." 

The latest dissolved oxygen readings at the same site show it is not "grossly contaminated as previously reported".

The report also details the work that has been done since 2011 to improve the health of the river. This includes the construction of fences along more than 100km of waterways in the catchment and the planting of more than 75,000 native plants.

Those plants are split between riparian areas and erosion-prone hill country, where more than 750ha of at-risk land has been protected.

Horizons freshwater and science manager Dr Jon Roygard said care must be taken in attributing trends to changes in management practices over such a short timeframe, but the results are encouraging.

"There is still plenty of room for improvement when it comes to water quality but I am cautiously optimistic that things are looking up across the catchment," he said.

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Other successes include improvements to wastewater treatment plants in Tararua, Manawatu and Horowhenua and the discovery and ongoing restoration of the North Island's largest known whitebait spawning habitat at Whirikino.

The Manawatu Catchment is now one of the most heavily monitored and studied catchments in New Zealand and Mr Thompson says this stands the Forum and community in good stead to make a change.

"We have an in-depth understanding of the challenges our river faces, allowing funding and effort to be directed to where it's needed most."

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