'Peeping Tom' Martin Carlin, who is 57 and from Ballyarnett Village was found guilty of voyeurism for the purposes of sexual gratification at Londonderry Crown Court on Monday.
Mr Carlin had denied the offence, which took place on August 24th last year while he was duty manager at the complex.
Carlin admitted being in a storeroom which connected male and female changing areas and hearing a woman shout: "Get out of there, you sicko," but denied that he had been masturbating.
The jury of six men and six women delivered a 10-2 majority verdict as Carlin sat impassively and the injured party wept.
Carlin has no previous convictions and was released on bail to reappear for sentencing on September 10th.
A spokesperson for Derry City Council later said that it is satisfied that measures are in place to ensure a safe and accessible environment for members of the public.
The Council said they co-operated fully with the police investigation and confirmed the staff member remains suspended until an internal investigation is concluded.