It’s About Lake Turn Over and It’s Coming to Lake Near You - Wilderness North

Celebrating 30 Years of Wilderness North  –          

It’s About Lake Turn Over and It’s Coming to Lake Near You

Almost all of the dramatic changes in northern lakes depend on changing of temperature. Area lakes now have a considerable layer of warm water with the surface nearly as warm as later summer – perhaps 20 to 21° C/70 °F.

Cooler temperatures in the next two months will reduce the warm water until the critical temperature of 4° C/39 °F is reached. Water is most dense at this point. Cool surface water sinks and is replaced with warmer water below the surface until the warm water is totally replaced. This “overturn” distributes nutrients and sets the stage for more cooling of the surface water. In most northern lakes winter ice formation takes place.

Ice coverage and thickness depends on the depth of the water and winter temperatures. Last winter was relatively mild. Lake Superior was mainly ice-free all winter (ice confined to bays and harbours) and the beginning of the shipping season in spring 2016 was the earliest on record in Superior and the other Great Lakes.

With the spring season and the Sun higher over the horizon ice melts and surface water slowly warms from 0° C/32 °F to 4° C/39 °F. Only when this “overturn” is complete will the top layer stratify. The less dense water floats on top and warms with late spring and summer conditions.

Different fish species seek different temperature layers. For example, trout species require cooler water below the warm stratified layer as the summer progresses.

Listen below to more of Graham’s fall weather thoughts:

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