Napier residents were asked to not flush their toilets, take a shower, wash their clothes or dishes on Wednesday, for fear of sewage spewing on to city streets.
Hawke's Bay has been inundated with rain, which leaks into Napier's sewage system, possibly leading to compromised stormwater inflows and a nasty overflow.
The stormwater also flows into the nearby Ahuriri Estuary, causing pollution in the popular recreation area.
The don't-flush request was issued about 10.45am, Wednesday.
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• Heavy rain, big swells, thunderstorms: Wild weather coming for already wet Hawke's Bay
• More rain on the way after heaviest falls in Napier and Hastings for two months
• Storm causes Napier building's ceiling to collapse
"Our wastewater system has been overloaded by over 24 hours of heavy rain," a Facebook post from Napier Council said.
"If we all work together to reduce the amount of wastewater we're producing, we hope to avoid an emergency discharge into the estuary.
"In order to prevent an emergency discharge from the network into Ahuriri Estuary, Napier City Council asks that the community flush toilets only when necessary, and hold off using showers, dishwashers or washing machines if possible.
"If an emergency discharge is carried out, this should prevent wastewater backing up and overflowing into city streets and properties.
"Toilets, showers, dishwashers and washing machines all drain into the city's wastewater network, which is also affected by infiltration of stormwater."
An update at 4.30pm said the situation had not changed.
Napier City's new mayor elect Kirsten Wise promised on the campaign trail to fix the problem.
"It's appalling that this hasn't already been addressed already," she said.
"The fact that Napier City Council is still discharging sewage into the estuary during heavy rainwater events, to me, is completely unacceptable.
"Iron Māori has had to change their course for their events this year, because they can't swim in the estuary."
She said Council had an Ahuriri master plan to address a number of stormwater issues.
"If I'm mayor all of those projects will be fast-tracked. This has to become top priority along with our drinking water."
It wasn't until 2015 that Napier stopped pumping raw sewage into the sea, the same year a 2015 Local Government Commission report said Napier had under-invested in vital infrastructure.