Hamilton City Council is requesting people do not swim near the Pukete Boat Ramp in the next few days and take precautions if they come into contact with river water in the area.
The warning comes after a pipe-fitting failure at the city's Pukete treatment plant may have resulted in a small amount of partially-treated wastewater entering the river.
The council's city waters manager Maire Porter says signs have been erected at the boat ramp following the incident, but indications are any discharge was relatively small.
"Late last night a plug on a pipe-fitting broke away, allowing the partially-treated wastewater to flow into the pump building. The discharge has flowed from the building and through to a stormwater system which leads to the Waikato River.
"While the spill was largely contained on site a portion may have entered the river, although this cannot be confirmed at this time," Mrs Porter said.
"Staff on site discovered the issue early this morning and have done a great job containing and cleaning up through the day. This issue is highly unusual and we are not aware of any similar incidents with this type of pipe-fitting.
"Any issue which may affect our environment or our river is a concern for us, and quick and decisive action by staff, in very hot conditions, has minimised the potential impact," Mrs Porter says.
The council expects the clean-up to be completed later this afternoon and after discussion with Public Health, Waikato DHB has issued the precautionary notice at the site. If people are exposed to the river water in the vicinity of the Pukete Boat Ramp it is recommended they thoroughly wash and dry their hands and any exposed cuts with soap and water afterwards.
People are also asked to avoid letting children play in the water or undertaking activities which result in them immersing their heads in water near the boat ramp.
The breakage at the plant affected one of five similar pumps and operations at the plant have not been compromised.