The Lake Michigan sea surface temperature is running 10 to 15 degrees cooler this year when compared to 2012. The below animation illustrates the large temperature difference between 2012 and 2013:
Here are the static images from the above animation:
To further show how anomalous Lake Michigan's surface water temperatures were in 2012, graphs of Lake Michigan's average surface water temperature over the last six years (2008-2013) and 2012 versus a 19-yr average are shown below (from the NOAA CoastWatch). Of note, in the former you can see quite a bit of variability over the last six years. Of which, 2012 shows some of the largest departures from the previous years (this is also seen with 2010). Note that the Autumn (Sep. - Nov.) and Winter (Dec. - Feb.) seasons depict some of the least variability in average surface water temperatures compared to the Summer, this could be attributed to many things. For one reason, there just hasn't been that much variability in regard to average temperatures in those time periods. The last image shows Lake Michigan's surface water temperature for 2013 so far versus a 20-yr average. Click an image to see a larger version.
National Weather Service - Milwaukee/Sullivan