Police in Hamilton arrested five people on Saturday at a series of unsanctioned street parties they say drew thousands.
Police say they received 49 calls about the parties near the McMaster University campus.
They estimate that between 8,000 and 9,000 people were in attendance at the peak of the revelry.
Officers say paramedics received 10 calls for service over the course of the gatherings, and two people were taken to hospital for public intoxication.
In addition to the arrests, police say they issued 10 provincial offence notices.
They say five people were charged under the nuisance party bylaw, which city council enacted last month and requires attendees to leave an area once their gathering has been deemed a nuisance.