E. coli levels in the Wairoa River were nearly four times the acceptable limit last week.
Warning signs dot the banks of the waterway cautioning people against swimming after high levels of E. coli were detected. The water is being tested this week to check whether levels are improving.
A Hawke's Bay District Health Board spokeswoman said E. coli levels should be less than 260 E. coli per 100ml, but last week's level was 970.
"The Wairoa River is often borderline and is graded as very poor by regional council monitoring over the summer swim season," she said.
"This week's test will help determine whether signage can be removed or needs to stay up, but it's a call the medical officer of health will decide based on the test results."
The elevated E. coli levels could have been caused by a number of factors, including contaminated run-off from farmland, birds, or other sources, and noted the situation followed recent rain events over the past two weeks.
The DHB had no reports of illness. It was waiting results of fresh sampling of the river undertaken by the Hawke's Bay Regional Council, expected to arrive today.
At this point, a HBRC spokesman said it was anticipated a clear reading would enable the signage to be taken down.
"A single clear reading is required as far as the swimming standard goes."
There are a number of discharges into the Wairoa River, including downstream discharges from Affco Wairoa, the municipal sewage discharge, stormwater drains, and both active and closed landfills near the mouth of the river.
The warning followed another issued last month for the Nuhaka River, near Mahia, where extremely high levels of faecal matter, 20 times higher than safe swimming guidelines, had been found.
Wairoa mayor Craig Little did not respond to requests for comment.
- If people did swim in the Wairoa River and develop diarrhoea and/or vomiting between one to two days afterwards they were advised to contact the on-call health protection officer at the Hawke's Bay District Health Board, phone (06) 834-1815.