People should not swim in, ski or row on, or even walk too close to the Waikato River because it is too polluted, warns the region's top public health official.
Waikato Medical Officer of Health Dell Hood has declared the region's famous river unsafe and to be avoided.
High faecal coliform counts have been detected in the river through Hamilton city.
Dr Hood said the public should assume the river water was unsafe.
She has even advised walkers who use riverside tracks not to go near the water when boats pass close enough to wet them with spray.
Persistently high faecal coliform counts in the river prompted an urgent meeting last week between Dr Hood, Environment Waikato and Hamilton City Council officials.
The council is considering putting warning signs along the river to warn that bacteria counts regularly exceed safety guidelines.
Dr Hood said the river was unsafe more often than not.
The high bacteria levels detected were an indicator of contamination by sewage or similar material.
"There must be assumed to be a risk of other harmful organisms such as viruses, hepatitis A, and protozea such as giardia and cryptosporidium being present in large amounts as well."