The Manuherikia River has the worst readings for E. coli out of all the rivers in Central Otago and the Queenstown Lakes district, the latest Land Air Water Aotearoa (Lawa) results show.

However, a regional water users group doubts the validity of the results, and says more testing should be done to determine the source of E. coli

The Manuherikia River was the only one out of 19 sites in Central Otago and the Queenstown Lakes district to record “C” and “D” readings in the most recent Lawa 10-year trend data, released earlier this year.

The 2009-18 readings, which show how the median of samples from the sites compare to other sites, rates the river as”C” at the Galloway measurement site and “D” at the Ophir site.

Rankings go from “A” to “E”, the latter being the worst possible and not recorded anywhere in Central Otago or the Queenstown Lakes district in the latest readings.

Both Manuherikia sites also had a five-year trend of “very likely degrading” ranking possible.

The Ophir site was also in the worst 50% for turbidity and total phosphorous, although in the best 50% for total nitrogen.

The Galloway site was also in the worst 50% for turbidity and total phosphorous, but the best 25% for total nitrogen.

Otago Regional Council strategy, policy and science general manager Gwyneth Elsum said a number of incidents of high E. coliconcentration during 2017 and 2018 had affected the trend of degradation in the Manuherikia over the past five years.

She said the council’s work to set a new National Policy Statement for Freshwater Management-compliant planning framework in the Manuherikia was continuing, through various groups and consultation.

The council’s “omnibus” plan change would also introduce a suite of provisions designed to “immediately fill the gaps in our water plan”.

“These provisions will target stock exclusion from water, farm environment management plans, and sediment run-off from new subdivisions or developments.”

However, Otago Water Resource Users Group (Owrug) chairman Ken Gillespie, of Oturehua, said he was “not convinced” the Lawa results were accurate.

He said detailed testing from Owrug and its members showed the Manuherikia was “in very, very good heart”, including through important indicators such as food sources for fish.

Mr Gillespie said elevated E. coli readings could come from testing done when river levels were high, for example following heavy rain, and that any E. coli was “not coming from farmers”.

He said it was “very easy” to determine the source of E. coli, and more testing should be done to determine whether the E. coli in the Manuherikia was coming from rural or urban sources.

The Omakau wastewater treatment plant is upstream of Ophir.

Central Otago District Council water services manager Quentin Adams said severe rain events in 2017 and 2018 caused the plant ponds to flood twice for two days in total.

“This caused overflows which would affect the results of sampling during this period.”

A number of improvements had been carried out at the wastewater treatment site, including new fully sealed lining of the ponds.

Other improvements were also planned to further improve the treated discharge quality, Mr Adams said.

E. coli is a faecal bacteria commonly found in the gut of warm-blooded animals, including humans. Land, Air, Water Aotearoa (Lawa) is a partnership between New Zealand’s 16 regional councils and unitary authorities, the Cawthron Institute and Ministry for the Environment, and has been supported by the Tindall Foundation and Massey University. To see the latest Lawa river quality results go to

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