CFD responded to the 600-block of North DuSable Lake Shore Drive for the boat incident, fire officials said on X just after 9:50 p.m.
A boat hit a breakwall near the Playpen and Ohio Street Beach.
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The Playpen is a popular area for boaters in the summertime, located between Oak Street Beach and Navy Pier.
Two people from the boat refused medical treatment, but one was taken to a nearby hospital in critical condition, and another was in serious condition, CFD said.
It's not immediately clear why the boat crashed.
Video of the scene was captured by a Citizen app user.
Five ambulances responded to the incident.
In June, a 58-year-old man died after falling from a boat in the Playpen.
And, in 2022, a woman lost both her legs in a boating accident in the area.