Watercare contractors have cleared a blockage in a sewagepipe which caused an overflow into the Wairau Stream at Milford on Auckland's North Shore.
A Watercare spokeswoman said the blockage was cleared last nightbut the cause had not yet been determined.
"They are going to carry out an investigation tomorrow," she said.
"They have people monitoring the site today and they have notified the council pollution control team."
Milford Residents' Association co-chair Debbie Dunsford said the problem appeared to have been fixed.
"I've been down there today and there was no smell or anything," she said.
"There is a pumping station down there, and as I drove past today I noticed there was a Watercare ute there with a man in it."