Lakes on Defrost: A Call for Ice Out Records

Ah, the birds are singing, the sun is still shining at 4:30 pm, and open water is starting to peek out from the edges of our icy lakes and ponds. Despite the false start to spring in February, Old Man Winter made a u-turn and brought us a March full of snow. But now it truly seems like time to pack up our skis and embrace the incoming mud season. And what better way to wait for warmer weather than to watch lake ice melt?


Ice beginning to recede on Lake Dunmore, Leicester.

In addition to its importance in understanding Vermont’s changing climate, tracking lake ice out is extremely useful for our aquatic biologists who assess lake water quality.  Shortly after ice disappears, lake surface water begins to warm. As the density of this upper layer increases to match the density of the colder water below, the once stratified lake begins to mix. This limnological phenomenon is referred to as lake turnover.  Phosphorus readings taken during spring lake turnover are indicative of the amount of phosphorus available for fueling plant and algae growth in the coming season. Lake turnover generally occurs 7-10 days after ice out, which gives our biologists just enough time to don their fashionable flotation suits and brave questionable weather for the sake of water quality. The Lakes and Ponds Management and Protection Program has conducted “spring phosphorus” sampling since the 1970s, which is vital for understanding how our lakes respond to changing climate and land use across the watershed.


A dedicated Lakes and Ponds Program biologist collecting water quality data on a typical Vermont spring day.

To help plan for the timing of lake turnover, the Lakes and Ponds Management and Protection Program is looking for ice out data. Ideally, we’d like to know the date when all ice has disappeared from a lake or pond; however, any observations you make regarding our thawing lakes would be greatly appreciated. Submit your ice out dates on the VT Lake Ice Out Survey or email Mark Mitchell.