A 17-year-old boy has been arrested on suspicion of rape at the Boardmasters music and surf festival in Cornwall.
Police say the teenager, from East Grinstead, West Sussex, has been released under investigation.
A 16-year-old girl from Somerset was attacked at the festival's campsite in Newquay.
Devon and Cornwall Police said inquiries were ongoing. Boardmasters said festival staff were helping police with the investigation.
A spokesperson added: "Across the entire site, there are staff specially trained to deal with emergencies including sexual assault and harassment.
"We strongly advise festivalgoers to report suspicious behaviour to any member of festival staff, they are there to help at all times."