Strains of the bacteria responsible for Legionnaires' disease have been found at a Swindon leisure centre.
Legionnaires' disease is spread by water droplets
Samples of legionella were found during a routine check of The Link Centre's water cooling system.
The centre has been closed as a precaution to allow sterilisation, although it is expected to reopen by Friday evening.
The council says the "minute" levels found present a very low risk, below that at which legislation requires any action to be taken.
Simon Birch, chief executive of Swindon Borough Council, said: "This is a clear demonstration of how our procedure for checking these systems is working effectively.
"What we have picked up is a very tiny level of the bug which presented a very low level of risk.
"That monitoring has allowed us to clean the water systems long before it became a problem."