Hastings District Council says a power outage was behind a sewerage manhole overflow earlier this month.
A council spokeswoman said the overflow of waste at Cooper St in Havelock North on August 6 was caused by the power cut that happened during the large storm.
"The pumps did not fail or break down, but they were affected as they run on power."
The council acknowledged that it had additional storage and back-up generators at pump stations but said the magnitude of the power cut suffered on August 6 meant some overflows were unavoidable.
"It is not designed and nor can it cope with the extensive power cuts, such as what we suffered when snow toppled a vast number of poles that day."