Lithgow’s JM Robson Aquatic Centre has been closed temporarily to sanitise the indoor pool after an incident on Tuesday.
Lithgow City Council operations manager Iain Stewart said the source of contamination was a child with a bleeding nose.
The 25m indoor pool is undergoing treatment to return the water to safe swimming conditions.
Mr Stewart said pool operators needed to be “ultra careful” to ensure the health and safety of all patrons.
He confirmed the centre will be operating as normal on Wednesday morning.