At least 1,500 people gathered on 400 boats in a canal in Berlin, according to German police, in an event that drew sharp criticism on social media.
Photos of the event - organised to support Berlin's nightclubs, artists and cultural festivals - showed hundreds of people crowding together with little social distancing.
The Berlin police said organisers ended the gathering after complaints about loud music and crowds. The meeting had been registered and accompanied by water police.
Participants had been asked before the event to keep distance from others and to stick to members of their household, according to Rebellion der Träumer, the group that organised the event.
They asked participants on Facebook to take face coverings and to treat people respectfully "so that it doesn't turn into a super spreader event."
Limits on outdoor gatherings were lifted in Berlin last week yet organisers of the event apologised for the "inappropriate endpoint" in front of a hospital and said they did not expect so many people to show up.
"We and the other actors involved should have done a better job," the organisers said.
It took until at least 9 pm on Sunday for everyone to leave the event.