River testing in the Murchison area during recent floods has revealed levels of E. coli bacteria in its four main rivers that make them unsafe for recreational use after rain.
The results have alarmed a kayak school owner in the town, who says the area has a "daunting" battle ahead to protect its water quality.
However, others say the results are not unexpected, and that farmers are working hard to make sure they comply with rules.
New Zealand Kayak School owner Mick Hopkinson said effluent built up on farms over dry periods and then washed into the rivers during floods or freshes.
Dairy farming had intensified in the area and farms had been manicured, which had added to the problem, he said.
"You've got fields like billiard tables, so we are whizzing down the river and these big green horizontal waterfalls are washing into the river. You can smell it, you can see it. Clean and green?"
The Tasman District Council has tested E. coli levels in the Matakitaki, Mangles, Matiri and Buller rivers when they were in flood on three to four occasions.
Each site had a reading at levels of over 1000 per 100 millilitres.
Water is considered unsafe for recreation when levels are over 550 per 100ml.
The swimming hole in Murchison known as the Eel Hole had readings of 1700 on January 3 and 591 on December 18.
It was the first time the catchment had been tested for E. coli.
"It's almost an argument for hardstand farming. It least you would be containing the effluent instead of washing it straight into the rivers," Mr Hopkinson said.
He was changing his website, which used to read that Murchison was an area where you could drink the water you paddled on.
Mr Hopkinson said a meeting about planting some streams in the Longford area was held last year, but now the tests showed that the area needing remediation had increased fivefold, which was "pretty daunting".
It had taken 10 years to make substantial improvements in the Sherry River catchment, but it was still not sorted.
Mr Hopkinson said there were two ways of attacking the problem - by taking the "softly, softly" approach or through legislation.
He believed stronger legislation was needed.
Tasman council environmental scientist Trevor James said the high reading was expected due to effluent runoff during freshes or floods.
He said rivers in the area had good water quality in normal or low flows, and it was only during high flows that E. coli levels were unsafe.
He said people should avoid swimming in the rivers for two days following heavy rain, a precaution that applied to most urban and rural environments.
He did not believe it was realistic to aim for E. coli readings in the catchment that matched the guideline for safe swimming following a flood, but it was possible to try to reduce the maximum and work to make the recovery time as short as possible.
Landcare Trust Nelson-Marlborough co-ordinator Barbara Stuart said the group was hoping to start a project next year.
She said runoff from land in areas that were intensively farmed was inevitable during big rain events, but farmers had measures in place to deal with small and medium-sized floods.
"And if they don't, Fonterra and the council are on to them."
She said it was easy to point the finger at dairy farmers, but the issue was about working constructively with farmers.
"It's about striking the balance between farming and tourism and the rights of all."
Nelson Marlborough Fish & Game officer Lawson Davey said some landowners in the area had done very good work, including building bridges and culverts.
His concern was with the 1 or 2 per cent who were dragging the chain.
Jane Field said she and her husband, who farm near the Owen Valley on State Highway 6, had taken up a Department of Conservation offer to plant trees, and planned to plant a couple of riparian margins along streams. Most of the margins on waterways on their farm were already planted.
She said most farmers were doing their best to fence off streams and build culverts, but it took time and money, and they were doing it as and when they could.
Tasman's sustainable dairying adviser Mirka Langford said Fonterra took its environmental sustainability seriously.
Mrs Langford said the council tests showed that the elevated E. coli levels were due to runoff as well as increased sediment loading, rather than point source discharges.
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