Police shut down an illegal forest rave attended by 500 people in the Brecon Beacons during the bank holiday weekend.
However, they were caught out when residents contacted Dyfed-Powys Police concerned about rising traffic on minor country lanes during the early hours of Sunday.
Officers attended the area and were faced with large amounts of people travelling to the site which was located within a forest belonging to Natural Resources Wales.
Police used Section 63 of the Criminal Justice and Public Order Act to set up vehicle check points within a five-mile radius of the rave site.
Some 200 to 300 people still remained at the site until later on and they were told to leave by a senior police officer.
“A certain portion of those attending were hostile to police attendance, directing abuse and threats towards the issuing officers,” a police spokesperson said.
“Following a 30-minute ultimatum to switch off the music and leave the site or face prosecution, attendees left the site.”
Police recovered three vehicles and their owners reported for unnecessary obstruction of the highway.
Several controlled drugs were seized from motor vehicles leaving the site.
Inspector Gwyndaf Bowen said: “Some of those that came to the rave were from as far afield as Essex and London.
“Social media was used to disclose the location at the last possible minute in order to prevent law enforcement taking preventative measures.
“We are very grateful to local residents for quickly reporting their concerns and allowing officers to take a practical approach to dealing with it.
“I thank local Breconshire officers for working significant hours in order to keep the area safe and end the unlawful gathering in a timely and peaceful manner.”
Officers reported there was no sanitary provision at the site and a large amount of litter was left behind.