Lake Natural History Note - Stratification

Warming spring temperatures lead to stratification of the lake. Photo by Carolyn Bates

In late April and early May the temperature of the lake at the King St. ferry dock in Burlington rose above 40 degrees for the first time this year. This signals the beginning of lake stratification. Water 39 degrees and colder is more dense than water 40 degrees and warmer. The warmer water sits atop the colder water unless wind and waves are strong enough to mix them. Through the summer the warm water layer grows thicker and mixing becomes less and less likely.   

The summer temperature of the cool lower layer is dependent upon the number of spring storms. If there were numerous spring storms, lots of mixing occurred and the lower layer is warmer. Few spring storms mean less mixing and a cooler layer. A 1979 study stated stratification in the Main Lake typically began in early June. However, over the last nine years stratification has begun as early as April 21st and only as late as May 24th.