Due to heavy rain over the last two days the Medical Officer of Health has advised people not to swim in Whangarei Harbour for five days and not to gather shellfish in the Harbour (including Mair and Snake Banks) for the next 28 days.

"We've made huge progress of the past four years so there was no uncontrolled spill this time, but our main sewage treatment plant did go into extreme bypass mode for two hours," said WDC Waste and Drainage Manager Andrew Carvell. "By this time next year we will have expanded the plant enough for extreme bypass to become a thing of the past."

"Under extreme bypass some wastewater going into the plant for treatment gets minimum processing before being discharged. In this case around 2% of the flow into the plant was only screened and settled before being discharged, and did not get disinfected.

"On the other hand, this storm has shown the major progress we are making across our sewerage system. An extension to the disinfection process completed last month reduced the extreme bypass volume from 6,400 to 930m3. The construction of an additional disinfection process to treat all wastewater is currently being designed, with a completion date planned for May next year."

During the storm the new $5 million Hatea wastewater storage and treatment plant passed its first real test with flying colours.

"The new tank stored 300 cubic metres of untreated wastewater that would have spilt directly into the Hatea River previously. This has since been pumped back into the wastewater system and treated at the Kioreroa Road wastewater treatment plant.

"The new plant that includes a large storage tank, ultraviolet light disinfection and a new pump, is now able to deal with a million litres of wastewater.

No other spills occurred although there was widespread pressure on the system.

Fast Facts

120mm rain fell in Hatea River Catchment during the weekend

$5M storage tank prevented a 300 cubic metre spill into Hatea River

Upgraded disinfection system at the wastewater plant reduced extreme bypass discharge from 6,400 to 930 m3

The additional disinfection facility currently being designed will come on line in May next year.