Aucklanders have been warned to stay out of the water at a slew of beaches across the region after heavy rain overnight triggered wastewater overflows, creating a "very high risk of illness" for swimmers.
MetService says about 50mm fell in downpours across the Auckland region in the early hours of Thursday morning, topping up dams and reservoirs but causing difficulties for the region's sewage infrastructure.
The wastewater system overflowed at several locations, sending sewage out into the Hauraki Gulf and running Aucklanders' chances of going for a swim - an activity that is now allowed after this week's drop to alert level 3.
One central Auckland local sent a photo to Newshub of a dark patch of what appeared to be polluted water off the coast near Bastion Point.
Watercare spokesperson Maxine Clayton confirmed overnight heavy rain had caused Watercare's Orakei Wastewater Pump Station to discharge into the sea at the Orakei Basin.
"This is a normal response in heavy rain events and is designed to reduce pressure on the wastewater network. The wastewater is heavily diluted by stormwater and the outfall pipe lies a long way off- shore," she said.
Safeswim gave the nearby Okahu Bay a black warning, indicating there's a "very high level of illness" for those who choose to swim there.
Okahu Bay is one of at least 14 beaches to be given the black warning, most of which were in central Auckland or on the North Shore. Dozens of other beaches were issued a red warning, denoting a high risk of illness.
Clayton says this is down to the huge amount of rainfall in the past 24 hours.
"We've received 70-100mm of rain in the Waitakere and Hunua Ranges, which has entered and overwhelmed [the] combined sewer system in older parts of the city," she said.
"In future, Watercare's Central Interceptor - a $1.2 billion super-sized wastewater tunnel currently under construction - will greatly reduce the overflows at this pump station by providing more capacity in the Orakei wastewater network."
For now, however, Aucklanders are urged not to swim at the beach for the next 48 hours due to poor water quality.
"This is not only caused by the presence of wastewater but also bird and animal droppings and diesel run-off from roads," she said.
However there are still some beaches that are safe for a dip. Most west coast Auckland beaches, and those from Hatfield's Beach north, are deemed a low risk of illness, as is Onetangi on Waiheke Island.
Anyone who sees what they believe to be polluted water or a wastewater overflow can call Watercare's pollution hotline on (09) 377 3107.