Abstract. Increasingly more leisure facilities, such as water parks or indoor swimming pools are being built in Poland nowadays. In order to ensure the air quality required by standards for such leisure facilities it is necessary to fit them with effectively functioning ventilation. For the removal of excess humidity, as well as chlorine ions occurring as a result of the disinfection of water as well as the carbon dioxide emitted by people using the facility, the ventilation system needs to be appropriately designed and efficient. For this reason, studies into the air quality in such facilities were undertaken. The paper presents the causes and consequences of the inappropriate operation and maintenance of ventilation systems in swimming pools. The study found that the causes of deterioration in the technical condition of the system which was operated in an environment with chlorine ions were: an inappropriate manufacture of its components and the wrong choice of construction materials for the given environment of operation. Furthermore, failure to follow the manufacturer's guidelines for the operation and maintenance of the components of the ventilation system greatly precipitated its degradation and the occurrence of sick building syndrome in the swimming pool. Solutions were found and proposed in order to improve the efficiency of the ventilation system in the given swimming-pool facility.