Cleaner water may be reason for dolphins

A cleaner Whangarei Harbour may be why a pod of dolphins has been using it as their playground.

Marine mammal expert Ingrid Visser has praised Whangarei District Council (WDC) for its new wastewater treatment process which has eliminated the largest pathogen source entering the harbour.

"Finally the dolphins that are frequenting our harbour are not being harmed by our pollution," she said.

At Wednesday's WDC infrastructure and services committee, councillor Sue Glen said six large dolphins were spotted in the harbour last week. "I wonder if they would have done that if it had been clean."

Ms Visser said the dolphins were likely to be bottlenose dolphins. She said while she has many years of records of dolphins and whales entering the harbour, it is now a healthier environment for them.

She said in the past numerous whales and dolphins had died in the harbour, but without testing for faecal matter she could not be sure that it was related to the pollution.

The treatment process includes 512 ultraviolet (UV) lamps that provides high intensity light that damages the bacteria or pathogen's ability to grow or replicate via a process not too dissimilar to that which causes sunburn, according to WDC waste and drainage manager Andrew Carvell.

It was switched on for the first time during the storm on August 2 and treated 23,600cu m of rain-diluted wastewater, killing 99.998 per cent of the bacteria that passed through it.

Up until now this water would have gone directly into the harbour.

"In the recent storm we estimate 726 trillion E. coli bacteria were killed that in the past would have gone into the harbour during a major rain storm," he said.

"The great thing about the new system is that we now have more treatment capacity than can actually be pumped to the plant, meaning everything will now be treated."

This $3 million project concludes Stage 1 of the council's wastewater improvement programme that aimed at dealing with the big sources of wastewater spills during storms.

Other projects completed in the past five years to reduce wet weather spills include the Okara pump station upgrade and the Hatea storage tank and treatment facility.

The Kamo Rd sewer will be upgraded and the wetlands along Kioreroa Rd are due to be renovated.