Photos show massive, maskless crowds as Lollapalooza begins in Chicago, sparking concerns of a superspreader event

Max performs on day one of the Lollapalooza Music Festival on Thursday, July 29, 2021, at Grant Park in Chicago.Photo by Amy Harris/Invision/AP

• Chicago's four-day Lollapalooza music festival returned Thursday after a year-long hiatus due to the COVID-19 pandemic.
• Attendees of the festival are required to show proof of vaccination or a negative COVID-19 test result no older than 72 hours.
• Unvaccinated attendees are required to wear a mask.
• A shorter and smaller festival in the Netherlands reported similar procedures and still saw a spike in cases, CNBC reported.

Despite a troubling rise in COVID-19 cases across the country, summer music festivals are back in full force, and Thursday marked the start of one of the biggest.

Chicago's four-day Lollapalooza music festival kicked off Thursday in the city's Grant Park, where roughly 100,000 attendees are expected each day.

The popular festival is back at full capacity after being canceled last year during the height of the pandemic. This weekend's event is expected to be one of the largest gatherings in the country since the pandemic began.

Amid concerns of rising COVID-19 cases and the spread of the highly transmissible Delta variant, festival officials are requiring attendees to show proof of vaccination or a negative COVID test if unvaccinated, according to the festival website. Those who have not been vaccinated are also required to wear face masks throughout the festival.