Gareth Vincent Hall, 22, is accused of grooming the school girl online, then travelling to Eugene, Oregon, where he hired a car and then took her to a hotel.
Hall worked as a lifeguard at the Caernarfon's Arfon Leisure Centre in North Wales, where police say he had "regular access" to young children, according to the Daily Mail.
Hall spent four days in the US before flying back to his home in Wales until last Saturday, when he returned to the US to allegedly meet a different girl.
Upon his arrival, he was arrested by officers from the Eugene Police Violent Crimes Unit as he got off a plane at Chicago's O'Hare Airport.
He was charged with three counts of rape, two further counts of serious sexual offences and one count of kidnapping.
Investigating officer, Jed McGuire, alleged that Hall had met the girl through "an online chat program" and that the pair had spoken for two months before meeting up, the Daily Mail reported.
"One of the things we hope to answer is why he travelled so far to meet with one person," he said.
A spokesman for police in Eugene said: "The Eugene Police Department is continuing the investigate the full range and scope of the suspect's activities.
"At this time, we don't believe there are any other victims in the local area."
Council officials in Wales have also launched their own inquiry into Hall's activities and urged concerned parents of children who use the pool to get in touch immediately.
A Gwynedd council spokesman told the BBC: "Whilst it would not be appropriate for us to comment on the details of the ongoing North Wales Police investigation at this stage, we can confirm that all relevant child protection procedures have been followed by the council in the management of this case."
The spokesman also confirmed that they were aware of the allegations in the US but said it was "not appropriate" to comment at this stage.
Hall is due to appear in court in the US on June 10, and bail has been set at $1.5m (£970,000).