July 21, 2000

     Minnesota Lakes

By July 4 this year a good share of Minnesota's lakes finally had reached surface water temperatures of 70 degrees, or a bit more.

Seventy degrees is the cut-off point for safe swimming.  At temperatures below 70 degrees most swimmers cannot exercise enough to maintain a normal body temperature and would be subject to hypothermia.

Most of our lakes in Minnesota are considered to be warm water lakes; that is, they warm to at least 80 degrees each summer.  Official surface water temperatures are taken down one foot in at least five feet of water.  The surface temperatures of Upper Midwest lakes usually peak during the last few days of July.

Many times we have recorded a surface temperature of 80 degrees or slightly above for Lake Minnetonka on late July days, while the water in the deeps held at 50 degrees.  These next few weeks lake surface temperatures hit their highs for the summer, and that means perfect swimming for everyone who likes this form of relaxation and exercise.