‘Worrying’ report on water in Moutere

A ‘‘bleak’’ report on the Moutere catchment, near Nelson, points to high water temperatures, poor invertebrate health, sedimentation and filamentous green algae along sections of its waterways.

The absence of giant ko¯ kopu, a native fish, was also noted in the Tasman District Council survey of stream health, which has been called worrying and bleak.

‘‘We have looked hard for giant ko¯kopu but haven’t found them,’’ council resource scientist Trevor James told the environment and planning committee at the end of 2018, when he presented the report.

The Moutere catchment was lowgradient and terminated in an estuary, giving it ‘‘potentially high’’ ecological value, James said.

A survey of the main stem and tributaries of the Moutere catchment was undertaken during the summer of 2016-17, with the aim of assessing water quality and stream habitat as well as the potential for restoration.

Comparisons were made with data from the council’s long-term monitoring site on the Moutere River at Ching Rd (Riverside) from 2012-18. ‘‘In all of this investigation, the biggest standout was the need to shade the river,’’ James said.

‘‘We had some pretty high [water] temperatures. We would go through an area that was really open . . . and the temperature would really start to rise every few hundred metres. Then we’d go through an area where it was shaded and the temperature would go back down again.’’

In his report, James says water temperatures were above 24 degrees C in much of the lower catchment, ‘‘high enough to cause significant adverse effects to stream invertebrates and fish’’.

The maximum was 25.7C at Wilson Rd, ‘‘with similar temperatures all the way to the estuary’’.

James told councillors the invertebrate health was ‘‘some of the poorest in our region’’, and there were also high levels of long filamentous algae growth in the water.

In general, apart from the main stem of the Moutere River downstream of Wilson Rd, stream habitat was reasonably good.

Another issue was sedimentation. The report outlines the potential sources as winter cropping and grazing, cultivation on steeper hill country, and ‘‘poor pine forest harvesting’’ coupled with poor riparian management, along with bank erosion.

‘‘Sediment source tracking carried out in the Moutere catchment showed the Moutere estuary is receiving a high proportion of sediment directly attributable to pine forest harvesting,’’ it says.

James told councillors that a compliance officer had been employed to work fulltime with the forestry sector.

He also spoke about bank stabilisation. ‘‘We identified through this study that there’s quite a lot of riprap going into the Moutere catchment,’’ James said, referring to a continuous line of rock to protect against erosion. ‘‘We have found around the district that riprap reduces the diversity of habitat and can really limit the ecological potential, so we’ve had a few field days with myself, river engineers and their contractors to see where we can look at alternatives.’’

Council staff proposed the development of a plan, involving the community, to look at the priority areas for catchment improvement ‘‘where we can get the best bang for our buck’’, James said.

Cr Dana Wensley called James’s report bleak and ‘‘very worrying’’.

She asked for a report on the next steps to mitigate the issues raised in the survey, a request that was supported by the rest of the councillors.