A Newtownabbey Leisure Centre has said a company hired to test for a bacteria which causes legionnaires' disease has admitted producing fake test results.
The Valley Leisure Centre was given the fabricated results over a six-month period last year.
Legionnaires' disease can be caused by breathing in water droplets contaminated with Legionella bacteria.
The centre employed east Belfast-based Healthy Buildings International Ireland Ltd, to carry out monthly checks.
The chief executive of Newtownabbey Borough Council Jacqui Dixon explained what happened.
"The council received an anonymous letter last week which made allegations about the testing of Legionella in our swimming pools. So we launched an immediate investigation into the matter," she said.
"As a result of the company who were involved in the testing admitted that our results were falsified for a six-month period during 2011."
The council has said the swimming pool does not pose a risk to the public, however the spa area remains closed while further tests are carried out.
Billy Webb, mayor of Newtownabbey, said: "I cannot believe any company would carry out such an action."
The Health and Safety Executive is now investigating what happened.
In a statement, Healthy Buildings International said they were in the process of issuing legal proceedings against a former employee.
They said they were investigating what they described as an anonymous and defamatory letter and would issue a fuller statement once legal clearance had been given.