Canterbury health officials are warning people to avoid the Avon River in Christchurch because of raw sewage leaking into the waterway.
A damaged sewer main in the suburb of Richmond has seen untreated sewage discharge into the river near the Swanns Rd bridge.
"Water quality in the Avon and Heathcote rivers rarely meets recreational water standards, but at the moment the Avon is particularly contaminated downstream of Swanns Rd and contact with water in the river should definitely be avoided," said Canterbury medical officer of health Alistair Humphrey on Tuesday.
The problem seems to have resulted from ongoing issues with underground wastewater and stormwater pipes damaged during the earthquakes, he said.
"We understand a large depression developed in the road over the top of a stormwater drain in Warwick St.
"This dip suggests that the sewer main has been dragged down and broken, and the untreated wastewater is entering at that point."
Dr Humphrey said there would be a temporary repair, but the permanent rebuild of the wastewater network in the area was expected to take until mid-2013.