The unidentified man, 31, appeared to be intoxicated when he toppled into the water, and was later hospitalized in good condition, police said.
He was rescued from the water by six friends, out for a bicycle ride, the Chicago Tribune reported Thursday.
"The guy kind of stumbled up to us, we just assumed he was drunk, and naturally you kind of stay away but we saw him as he was heading to the water," rescuer Nicholas Welker said.
Welker and friend Brandon Cruz dived into the water to save the man.
"He kept trying to save his phone. He dove under to get his phone and then he kind of gave up swimming," Welker said.
They brought the man to a nearby dock, and paramedics took him to the hospital, the newspaper said.