Police launched an investigation after an attack on a 16-year-old girl was reported at around 9pm on Sunday.
A 17-year-old man was arrested in connection with the incident but has been released pending further inquiries.
Part of the park near Motherwell was cordoned off on Monday while officers investigated the area.
A Police Scotland spokeswoman said: “A 17-year-old man has been arrested and released pending further inquiries.
“Inquiries are ongoing.
“Anyone with information is asked to contact 101.”