A 17-year-old has been arrested after a page was set up on social networking site Facebook to plan a fight at Portishead Carnival.
The youth from Weston-super-Mare was arrested on suspicion of incitement to cause violent disorder and later released on bail.
The arrest was made by officers investigating a fight in Pill on 5 June.
Two arrests have already been made in connection with the incident.
Insp John Owen, of Avon and Somerset Police, said: "We are taking this incident very seriously and are warning youngsters that we will not tolerate any anti-social or violent behaviour at Portishead Carnival.
"I would like to reassure local residents that we are working hard to ensure the carnival will remain a peaceful and safe family event."
The Portishead Carnival is due to held on 19 June.