deadly boating accident on lake Michigan near Chicago. Four people jumping into the water from their burning boat. All of them with life vests. Only one rescued so far. And tonight, why those vests... See More
deadly boating accident on lake Michigan near Chicago. Four people jumping into the water from their burning boat. All of them with life vests. Only one rescued so far. And tonight, why those vests might not have been enough. Here's ABC's gio Benitez. Reporter: Search teams from Chicago combing lake Michigan today, hoping to spot those two missing boaters before sundown. We're searching a very large area out there. Reporter: The boat was returning to Chicago from new Buffalo, Michigan, last night, when it started to sink just before nightfall. With no working radio on board, they set off flares, but the boat was too far offshore to be seen. That's when they put on their life jackets and braved the frigid lake through the night. At dawn, a nearby boat spotted one of the victims about six miles offshore Apparently the boat caught on fire. It was heavily involved in smoke. The -- it was taking on water and the boat was sinking. Reporter: Dazed and confused from hypothermia, the man told rescuers there were three others. When the people did enter the water last night, they were separated. It was nighttime, so, they could be, you know, at this point, miles apart. Reporter: He was rushed to the hospital in critical condition. About an hour later, another boater was rescued, but she did not survive. And tonight, we're told the water was about 60 degrees this morning, but even if the missing boaters are wearing life vests, hypothermia can set in within just an hour or two, at that temperature. So, David, finding them quickly is absolutely critical tonight. All right, gio, thank you.
This transcript has been automatically generated and may not be 100% accurate.