Fatbergs, a build up of slime and debris that blocks sewerage pipes, have been found in a sewer main in Dannevirke.
They've been causing numerous issues, including an infestation of rats.
It has prompted calls for residents to be sensible with what they pour down sinks, or flush down the toilet.
Watercare wastewater manager Shane Morgan says the fatbergs are "just an accumulation of fats, oils, greases, plastics, papers and all the kind of debris down a sewer system".
"The problem with a fatberg is it's so large that it causes a substantial problem for the utility."
Despite Auckland sewerage systems not having "too much of a problem" with fatbergs, Mr Morgan warned of flushing items which can cause issues down the pipes.
He said the frequent uptake of wet wipes being disposed of down toilets was a big issue.
"They're absolutely not flushable. That wet wipe travels down the pipe, picks up all of that debris and it balls it up... it causes a substantial problem for us."
Mr Morgan said he's seen toys, false teeth, money, and even a passport down in the sewerage system.
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