"Police attended however there were no reports of any fighting, more a loud party and the organisers were spoken to," Inspector Henrikson said in a statement.
"Approximately an hour later though it was a different story with even larger numbers of drunken youths out on the street fighting.
"Our Tactical Response Unit approached the scene but were pelted with bottles and other missiles requiring them to retreat, call in for reinforcements and don protective public order equipment."
The area was cordoned off and four arrests were made, including one charged with assault with a weapon, police said.
"Some of the dispersed youths turned their anger on an ambulance near the entrance to the lake and it came under attack from flying bottles necessitating the crew, who were on station to treat any injured members of the public, retreat to a safer location."
A nearby event centre went in to lockdown until the disorder was under control.
