The Far North District Council is defending its wastewater treatment works in the Hokianga as a protest hikoi is set to march on Waitangi to highlight the issue.

A protest march on Waitangi Day will aim to focus council and central government attention on what organisers say are sewage woes afflicting the Hokianga Harbour.

Some council wastewater treatment plants serving Hokianga towns were well past their use-by date, polluting a historically and spiritually significant harbour, locals said.

But the FNDC says it's not correct to say it is not doing anything about the sewage issues.

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Andy Finch, general manager – infrastructure and asset management, said four treatment plants discharged into the harbour after being treated via ponds and wetlands to stabilise the wastewater. They service Kaikohe, Kohukohu, Rawene and Opononi-Omapere.

Each has different NRC consent conditions on measures such as nitrogen levels, E. coli counts and total suspended solids. Rawene has the strictest consent conditions.

''At times, individual measures have been breached. There is one abatement notice in place for significant non-compliance with bacteria limits at Opononi-Omapere. However, at no time have breaches resulted in raw or untreated sewage being discharged from any of the ponds into the harbour,'' Finch said.

''Considerable work has been undertaken to rectify problems at Opononi-Omapere. The wetland was de-sludged and replanted in 2015 and the detention pond de-sludged in 2016. In 2018 the aerated lagoon and the detention pond were also de-sludged. A new brush aerator for the aerated lagoon ... will be installed at this facility in the coming weeks.''

There were no significant problems with the Rawene plant and breaches of its consent conditions were infrequent.

Finch said the resource consent for Rawene directed the council to investigate and report on options for the future treatment and disposal of wastewater, which it was doing.

At Kohukohu, septic tanks on each property are due to be emptied in the coming months, which is done every five years.

At Kaikohe, changes will be made to the pond outlet structure to reduce the carryover of suspended solids into the wetland.

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''Many activities, including farming, forestry, household septic tank systems, and land development, affect water quality in the harbour. Exactly how treated wastewater impacts the Hokianga is not well understood. To fill that knowledge gap, the council this year plans to map and model how treated wastewater discharges are distributed by tides and currents in the Hokianga.''