Cooling water temperatures signal fall turnover
We are coming up on an important transition time for our area lakes. We are approaching "fall turnover". The turnover time is when the mass of the lakes mixes and the water on the bottom of the lake actually comes to the surface and all water in the lake mixes. We can know the lake has turned over, as the water will actually smell foul, like rotten eggs, for a day or two. The water will be very cloudy for a few days before becoming clear. You may notice foaming at some of the wind blown shoreline areas. It is not uncommon after turnover to see dead fish come up from the bottom and get deposited on the shorelines.
Not all the lakes have a turnover event. Lakes in our area that are about 25ft or less will not usually experience a "turnover" effect, as they are constantly being mixed throughout the summer and fall by strong winds. Lakes that are deeper will stratify as they warm through the summer. The upper layer is usually about the top 25-35ft of water in most of our area lakes. A layer called the thermocline will occur during the summer that will separate the top and bottom columns of water. The oxygen and temperature are comfortable for baitfish and fish in the upper layer of water. Under the thermocline is cold, non-circulating water with low oxygen levels and is not comfortable or baitfish for fish.
In the fall, as water cools, it gets heavier and the wind will mix it enough to breakdown the thermocline layer. The whole mass of the lake mixes and creates the "turnover". After the turnover, fish can be very deep in the lake in areas that they never spent time during the summer, as oxygen levels are comfortable throughout the whole system.
Not all lakes that have a thermocline in them turn over at the same time. The size, surface temperature, and wind exposure will all be a factor. This is a good thing for us, as we can pick lakes that have not yet turned over, or lakes that have turned over to fish, and avoid the lakes in the midst of their turnover cycle.
Fish are extremely neutral to negative in their feeding when the lake is in the middle of a turnover. It can take from a couple days to as long as a week for the bite to get straightened around again on those lakes.
We are close to this turnover time as water temperatures have dropped below 60 degrees. When the surface temps get around 50 degrees the lake is ready to do its thing. It can happen earlier, of course, if we get severe winds when the surface temperatures have been dropping. As the daylight hours continue to get shorter and the overnight temperatures get cooler the surface temperatures of the lakes will continue to drop. The sun isn't nearly as powerful now. Even the warm weather we have had this last week has slowed the lakes cooling process, but they continue to cool. With the forecast getting cooler this next week, shorter daylight hours, and cooler nights, we are getting close to turnover time for our area lakes.
You can still catch fish shallow now, but check deeper water after turnover.
(Laabs runs Brad Laabs Guide Service in Detroit Lakes.)