Tauranga's sewer system has overflowed into the Waikareao Estuary.
Heavy rain overnight caused an overflow from a manhole at Third Avenue West.
A Tauranga City Council spokesperson said the cause of the overflow was a system overload where a large amount of water from the heavy rain inflowed into the wastewater system to the point where the pipes became full.
He said the overflow probably lasted for about an hour.
Water quality samples have been collected from the estuary for testing. The results are due on Thursday.
Health warning signs have been installed at Third Ave, Chapel St, Maxwells Rd and Sulphur Point.
Meanwhile there was a smaller overflow in Bethlehem last night.
The overflow at Sterling Gate Drive has affected the stormwater ponds in that area.
The spokesperson said this was probably caused by blocked pipes.
This is still being investigated.
Health warning signs are in place around the area.