Turnover

 

It's fall and I get asked all the time if the lakes up here in northern Wisconsin have "turned over" yet. This is probably the single most misunderstood concept of fishing and the yearly ritual can prompt some serious changes in your fishing tactics.

First of all, the direct answer to the question is, we're nowhere near yet. It's early September and water temperature has everything to do with turnover. Look for temps in the mid-50s to get things going. Here's an explanation, and the key to this question is how water density varies with water temperature. Water is most dense (heaviest) at 39º F and as temperature increases or decreases from 39º F, it becomes increasingly less dense (lighter). In summer and winter, lakes are maintained by climate in what is called a stratified condition. Less dense water is at the surface and more dense water is near the bottom.

 

During late summer and fall, air temperatures cool the surface water causing its density to increase. The heavier water sinks, forcing the lighter, less dense water to the surface. This continues until the water temperature at all depths reaches approximately 39º F. Because there is very little difference in density at this stage, the waters are easily mixed by the wind. The sinking action and mixing of the water by the wind results in the exchange of surface and bottom waters, which is called "turnover." A couple telltale signs if a lake is turning over are clear lakes become muddy and there's sometimes an odor to the water from the decaying vegetation from the bottom that's now making its way to the surface.

 

During spring, the process reverses itself. This time ice melts and surface waters warm and sink until the water temperature at all depths reaches approximately 39º F. The sinking combined with wind mixing causes spring "turnover." This describes the general principle; however, other factors including climate and lake depth variations can cause certain lakes to act differently. Take the Eagle River Chain, for example. It doesn't turn over because it's moving water.

 

I mentioned the affect on fishing...a lake in the process of turnover has the oxygen level consistent throughout the body of water and that allows the fish to really scatter because it's now comfortable to travel at all depths. That makes our job a little tougher to find them, no matter what species. But, the feeding pattern remains unchanged so find the baitfish or the structure and you'll find what you're looking for. You'll also have to navigate through some pretty ugly water because most of what's been sitting on the bottom all season is now floating to the top. It can get pretty yucky sometimes. On the upside, this is also prime time to begin using larger baits and suckers for muskie. The feeding frenzy is on for the big fish in fall and trophy hunting is in full swing until the end of the season.

 

Good luck this fall!