Survivors said the Coast Guard rescued them, just in the nick of time.
What sounded like a dangerous situation, ended with no injuries, fire officials said.
The Chicago Fire Department said a boat with 11 people on it started filling with water about 2 a.m.
RELATED: Father of missing boater continues search week after boat capsizes near East Chicago Marina
That's when the Coast Guard responded, bringing the group to Calumet Harbor.
"Three more minutes, and we wouldn't have made it, but thank God to the Coast Guard," Vivian Allen said. "They saved our lives. We are here to tell our story, and we are going home."
Everyone declined to be taken to the hospital and were uninjured, according to CFD.
"I'm still in a little bit of shock," Nicole Gooden said. "Our boat was about to sink; water was coming into the boat. It's unexplainable right about now. I mean, we're joking and laughing because we're happy we survived, but we also hit a rock or something out there. It was just hectic. And it took forever for them to get to us."
Gooden said the boat sunk so low, they were able to touch the water while standing on the top of the vessel.
"It was traumatic," she said.
A partially-capsized boat was visible in Calumet Harbor about 6:30 a.m., but it was not immediately clear if it was the boat involved in the incident.
The Coast Guard is out on the water this weekend, looking for people drinking and boating, but that does not appear to be part of this investigation.