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As part of its obligations under the Resource management Act 1991, the Dunedin City Council has regularly monitored some 60km of coastline stretching from Akatore in the south to Victory Beach in the North (Figure 1) for over ten years.

Sites include:

• Akatore
• Taieri Mouth
• Bruce Rocks
• Brighton
• Black Head
• Second Beach
• Lawyers head
• Smaills Beach
• Boulder Beach
• Sandfly Bay (south end and north end)
• Allans Beach
• Victory Beach

View monitoring map (JPG, 48kb, open in new window)

This monitoring has revealed no adverse environmental effects attributable to either the Green Island sewage outfall at Waldronville or the Tahuna sewage outfall west of Lawyers Head. All sandy and rocky shore communities examined remain healthy and exhibit no change outside natural variability.

Mussels and seawater are regularly sampled at each of the above sites and analysed for microbiological contamination. To date, these analyses have shown that there is some contamination of shellfish at Second Beach, Lawyers Head, Smaills Beach and Boulder Beach on rare occasions. All other beaches are essentially free from microbiological contamination that could be linked to sewage.

The commissioning of the new extended wastewater outfall from the Tahuna wastewater treatment plant has led to a decrease in bacterial levels on Second Beach, Lawyers Head, Smaills Beach and Boulder Beach bacterial such that an acceptable recreational standard is now the norm.

Whole effluent toxicity testing (WETT) is carried out on Dunedin effluent annually by NIWA. This tests the toxicity, or effect, of the treated wastewater discharged from the two wastewater outfalls on a variety of small marine organisms. This testing shows that the wastewater at both sites is sufficiently dilute within the allowable mixing zone as to have no effect on local marine life. Indeed, divers examining the Green Island and Tahuna outfalls report healthy and varied marine life, including sponges, blue cod and crayfish, actually living around and under the outfall diffusers.

Additionally, the discharge consent for the Green Island WWTP requires that water quality to the east and west of the Green Island outfall be monitored annually. To date this monitoring has shown that nutrient levels in the water either side of the outfall has nutrient (nitrate and ammonia) levels no different to levels in the coastal waters off other parts of the Otago coastline.