UPDATED 07/17/12 11:38 a.m.

CHICAGO (CBS) — A 6-year-old boy was in serious condition Tuesday morning, after being pulled from Lake Michigan by his even younger brother at the South Side’s Rainbow Beach.

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As CBS 2’s Susanna Song reports, the witnesses say the boy’s 5-year-old brother pulled him out of the water and rescued him Monday evening. And he wasn’t the only one who stepped up to the plate and jumped into action.

Krystal Bishop, who had recently learned CPR for her job as a steel worker, also rushed to help. She said she heard commotion from the lake as she sat at Rainbow Beach off 77th Street.

Bishop performed two rounds of CPR on the boy, as lifeguards were off duty at the time. Lifeguards are only on duty from 11 a.m. to 7 p.m.

Paramedics arrived around 7:20 p.m. and took the 6-year-old boy to the Comer Children’s Hospital at the University of Chicago Medicine.

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“I just ran over to him, because I know, click, you’re CPR certified, go do what you can do. That’s it,” Bishop said.

She said she didn’t think it looked good for the small boy as she performed CPR.

“I thought he was gone. I thought that little boy was gone,” Bishop said. “He was limp; foam coming out of his mouth.”

As of last report at 11 a.m. Tuesday, the boy remained in serious condition.

It is unclear if the boy’s parents were around, or if the boys knew how to swim.

The rescue came just a day after a 44-year-old woman drowned in Lake Michigan near Lake Forest. Her body was found about 2 1/2 miles offshore late Sunday morning, following an extensive search by the U.S. Coast Guard.

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With the temperature Tuesday expected to approach 100 degrees, a lot of people are expected to gravitate toward the lake again. Officials advise everyone to make sure they keep a close eye on their loved ones if they plan to swim.