Further water quality sampling is underway in Tasman's Kaiteriteri after elevated levels of bacteria were found in a part of the town's sea.
Over the weekend, Tasman District Council warned people not to swim or take shellfish from Stephens and Dummy Bay after the results of water quality monitoring tests carried out last week.
The council said the bacteria could cause some people to become ill and so people should avoid swimming or taking shellfish from those areas until 20 January.
The Stephens Bay wastewater network had been checked but the source of contamination had not yet been found, the council said.
However, the council believed it may have happened during last week's rain.
It said it would carry out further water tests and investigation work today.
Toxic algae in Wai-iti River
Meanwhile, toxic algae in the Wai-iti River near Nelson is at high enough levels to pose a serious risk to dogs and other river users.
Tasman District Council environmental information manager Rob Smith said the algae was a problem in the lower reaches of the river, and other rivers in the region could also be affected.
It happened during long periods of low flow in rivers and was made worse by fine sediment.
Smith said all dog owners and parents should become familiar with what the algae looked and felt like.
It can have a distinctive musty smell which is attractive to dogs, but it is usually only a problem if ingested.