A third person was injured and remained hospitalized Sunday night.
One accident happened on Lake Michigan near DuSable Harbor, and the other happened on the Little Calumet River at 127th and South Michigan.
On Monday, search crews were still looking for a missing boater in the Little Calumet River accident.
A boat capsized Sunday morning throwing two people into the water.
Ronald Johnson, 62, of Chicago died. The other man's identity is not known.
The skies were clear and the wind was blowing slightly Sunday morning, making it an ideal day for sailing. However, one boat in DuSable Harbor never made it out, as two people went overboard.
Witnesses Dennis O'Leary and Jennifer Carlson say the boaters went in the lake after they were trying to retrieve something that fell in the water. They were able to help pull one boater aboard.
"We were out in the harbor and noticed two swimmers asking for help. My girlfriend and I circled around and helped him aboard," O'Leary said.
"He steered the boat and got me closer, and I was able to drag the guy out the boat hook," said Carlson.
Unfortunately, the second person had already gone under, and there was nothing O'Leary or Carson could do. The fire department's scuba team tried their best to save him.
"There was a second person missing in the water. [In] a joint effort, police Marine unit and the Chicago Fire Department put divers in the water. They were able to located the victim. That victim was also transported to Northwestern Memorial Hospital," said the Chicago Fire Deparment's Ron Dorneker.
However, it was too late. The second boater died. He is identified as 52-year-old Michael Vergauwen.
About 45 minutes before the Lake Michigan accident, the Chicago fire and police departments were on the scene of another boating accident. It was first reported to 911 that two boaters were clinging to their 15-ft. boat, after it capsized.
"After talking to witnesses, the people were never clinging onto boat, they apparently went directly into the water and were never actually holding on to the boat," said Chief Petty Officer David Allen of the U.S. Coast Guard.
Both boaters went under water. Police were able to recover one body shortly after the incident but not the other.
The Coast Guard says in both of Sunday's boating accidents, no one was wearing a life jacket.
"A basic, standard, most-economical life jacket will keep you afloat, keep your head out of the water, and save your life," said Officer John Stajcic of the Chicago Police Marine Unit.
Police say many boaters do not think of wearing life jackets because they have the impression that they can swim. Nevertheless, police and the Coast Guard warn boaters that water conditions always change.
The Coast Guard says the inflatable jacket is more expensive than other jackets, but it is ideal for people who think life jackets are too bulky or uncomfortable.
The law says if you are on a boat, there must be one life jacket for every person on board, and the jackets should be easily accessible.
Wearing a life jacket on a moving boat is mandatory for anyone under the age of 13.