Auckland Council says the water used to fight the fire at SkyCity's convention centre was "sufficiently diluted" by the time it was pumped into the ocean.
An estimated 27 million litres of water was used to fight the blaze, with 15 to 20 million litres of that reaching the sea, said Nick Viger, head of Auckland Council's Safeswim programme.
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Although the tests showed the water had "elevated levels of several contaminants" expected from burning materials, the water was "sufficiently diluted by the time it reached the waterfront to cause no long-term impact on marine life or water quality," Viger told reporters on Friday.
Auckland Council freshwater scientist Dr Coral Grant said testing showed the water had "low to moderate toxic effects", but was "very localised" to where the water was pumped into the sea.
Much of the contaminants came from burnt bitumen and plywood in the ceiling of the building, with others coming from water around cars in the basement containing oil and petrol, Dr Grant said.
Although the council initially issued a warning advising people not to swim around the outfall areas, Viger said the risk to health had diminished significantly after several tidal cycles and it was now "business as usual".
The fire brought central Auckland to a standstill as it burned for three days last week.
As well as the SkyCity precinct, numerous surrounding businesses and streets were evacuated, with the long-term economic impact expected to be in the hundreds of millions of dollars.
The cause of the blaze is still being investigated.
Newshub.
