Rosser1954, CC BY-SA 3.0, via Wikimedia Commons
Residents are curious about the white foam that appears along the shoreline, so we asked our local Lac Le Jeune Conservation Association water monitoring expert to explain! Also, the fly fishers out there might want take note of where the trout seek optimum oxygen levels -- explained below.
From Hugh Burton
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This is not an unusual phenomenon particularly at this time of the year.
Our lake is at its highest point in the production of living organisms, most of which are going through their respective life cycles, which include the production of metabolic byproducts like proteins and carbohydrates. Part of these cycles includes death of these organisms, which as they decay adds to the soup of suspended molecules.
When we get a good brisk wind, particularly one that causes the wave crests to break, we get a foaming action. Think of beating egg whites.
At this time of year there is another phenomenon that increases the chance of foaming by restricting the water volume in which the high level of biological activity is occuring. This is the thermocline.
Mike Brugger and I did a lake monitoring run this morning and found that there was a very strong 4m thick thermocline starting at 8m below the surface. This is virtually like putting a 4M thick horizontal tarp down at 8m, thus dividing the lake horizontally in two distinct sections.
Above the thermocline the oxygen level was 34% and the water temperature was 17C. Below the thermocline the oxygen level was 9% and the temperature was 8.1C.
Added to this, is the depth to which the light is effectively penetrating, which on this date at this location was 5M.
So, most of the intense oxygen dependant and light dependant biological activity at the moment is restricted to the top 5 to 8m of water.
In other words ideal conditions for a good frothing given the right wind. It is non toxic unless there is growth of certain toxic algae or bacteria, which fortunately our lake does not cultivate.
* Note 1: the thermocline is defined by a drop of one degree Celsius over 1 meter. In this case there is a drop of 8 degrees Celsius in 4 meters.
* Note 2: our trout need at least 30% oxygen to survive. So, they are restricted to the top 8m.
