What’s the highest Lake Michigan water temperature recorded at Chicago?

Dear Tom,
What’s the highest Lake Michigan water temperature recorded at Chicago?
— George Kuritza
Dear George,
Rebounding from icy 32-degree late-winter water temperatures, August is typically the month when the lake reaches its highest levels here. Readings usually top out in the upper 70s but can reach the lower 80s in the warmest summers. However, area swimmers can still be in for a “cold-water surprise” this time of the year. In a process known as “upwelling,” offshore winds carry the warm surface beach water out into the lake, replacing it with much colder bottom water, causing the water temperature near the shore to crash into the upper 50s or lower 60s. Readings quickly rebound back into the 70s, though, when east or northeast winds return the warm surface water to this side of the lake.
Rebounding from icy 32-degree late-winter water temperatures, August is typically the month when the lake reaches its highest levels here.