Water quality testing in Auckland's Waitemata Harbour following last week's SkyCity convention centre fire has revealed no long-term impact on marine life or water quality.
While the water had elevated levels of contaminants, which was expected to be present from burning building materials from the fire, the water was sufficiently diluted by the time it reached the waterfront, Auckland Council said in a statement.
Overall, an estimated 27 million litres of water was used to fight the fire - which began on Tuesday afternoon and continued to burn for five days - an estimated 15 to 20 million litres of which entered the harbour.
Of that amount, approximately eight million litres were collected in the basement, and 1.8 million litres went into the harbour over a 20-hour period.
After testing, the decision was made to pump the residual wastewater into the wastewater network, to be taken to the Māngere Wastewater Treatment Plant for treatment.
"Our focus is to prevent contaminants from entering the harbour, but during an emergency event like last week, it is not always possible," Auckland Council principal freshwater scientist, Dr Coral Grant, said.
"In this instance, water entering the harbour is unlikely to have had any major effect on water quality or marine ecosystems," she said.
"During the event, there may have been some ecological effect, but this will have been short-term and localised."
Ecotoxicity testing was carried out by NIWA, using samples from the site and the stormwater outlet, Dr Grant said.
"As expected, during the firefighting event. the water supplies from the fire site were moderately harmful. However, given the substantial dilution of the water once it entered the harbour, there would have been minimal impact to marine life beyond the initial mixing zone of 10 to 100 metres from the stormwater outlet and no long-term effects.
"While there is potential for some contaminants to bind to sediments and be ingested by filter-feeding shellfish, it is unlikely to be an issue as the Viaduct Harbour basin and port already have a degree of contamination."
Any long-term effects would likely be confined to the sediments in the immediate vicinity of the discharge points, Auckland Council Safeswim programme manager Nick Vigar said.
However, some of the affected the sediment will be dredged in the next fortnight as part of the new Americas' Cup facility.
"All this 'mudcrete' to immobilise any contaminants and sent to landfill," Mr Vigar said. "None of these sediments will be disposed of in the marine environment."