Three men have been arrested and bailed after a group of "at least" 15 people were seen fighting at an arboretum.
Officers armed with stun weapons were sent to Lincoln Arboretum on Monks Road at about 17:45 BST on Sunday, Lincolnshire Police said.
Members of the public called police after a man was spotted with what was thought to be a machete.
Fighting continued in a nearby shop with police having to "lockdown" the area to protect the public.
The men, aged 18, 19 and 22, were arrested on suspicion of affray and have been subsequently bailed, police said.
Insp Julia Baker, from Lincolnshire Police, said "at least" 15 people, all believed to be known to each other, were involved in the fighting in and around the arboretum.
"We had to lockdown the arboretum to protect people, so that innocent members of the public weren't injured," Insp Baker said.
The brawl happened in the same week as outdoor Covid restrictions lifted, with police saying it was a "shame" innocent members of public were "worried" and "upset" by the group.
Fighting continued at a nearby Co-Op store on Monks Road, police added.
A dispersal order has been put in place in the area to stop people congregating in groups.