Coleraine Borough Council said the leisure centre was closed on Monday after preliminary test results showed that the showering system was infected.

“All relevant agencies have been consulted and are advising council staff on how to proceed,” said a council spokesman. “Works have already commenced to disinfect the system.”

He said the leisure centre will remain closed until the council is satisfied that all tests results are clear.

Councillor John Dallat expressed relief that the bacteria was detected without any casualties and that the leisure centre was subsequently closed for disinfection.

“While this is disappointing news it shows the absolute need to carry out regular sampling to ensure the health of the public is protected,” he said.

“I have asked for a full report on the possible explanations for the presence of the contamination and the steps that should be taken to ensure that public confidence in this excellent facility is maintained,” he added.

Legionella is a bacteria found naturally in rivers, lakes and reservoirs, usually in low numbers. But water temperatures between 20 degrees and 50 degrees centigrade favour the bacteria’s growth.

Spread through the air via tiny water droplets, though this appears to happen only very rarely, the bacteria causes Legionnaires’ disease.

The early symptoms of the illness may be flu-like with muscle aches, headaches, tiredness and a dry cough followed by a fever, chills and occasionally diarrhoea and possible pneumonia. Symptoms usually occur three to six days after exposure.