If the northern part of the country where I live (Wisconsin) and annual event occurs typically right around the first week of October. This event is called "turnover". I am sure that cooler temperatures effect the water in other parts of the country, but I can't speak to the severity of the effects in other areas. While this event occurs ever year, it is not uncommon to find fisherman who aren't exactly sure what it is, and how it effects fishing. First, lets describe what turnover is for those that do not know. Turnover involves the physics of water temperature and how it relates to weight, i.e. cold water weighs more than hot water. This is because the water molecules of hot water are further apart than that of cold water, so closer packed molecules result in more weight. Enough on the physics lesson. During the summer months the surface water is constantly being hit by the warm sun, and therefore as described above, the warm water stays on top (it weighs less). You probably have dived into the water and just a few feet down discovered that the temperature dropped significantly. That is normal in the summer time. When fall arrives, the opposite effect starts to happen. The surface begins giving off heat into the air. If you fish in the fall , it is not uncommon to see fog or mist coming off the water in the morning. That is because the air is colder than the water and like like a breath on a cold mirror, the water is literally condensing in the air causing the mist. As more heat is given off to the air, the surface water gets colder and heavier. Eventually, the surface water actually gets colder than the water at the bottom, and it sinks raising the bottom water to the top. Literally turning the lake over, bottom to top, top to bottom.
The transition during turnover is just that. It isn't an immediate effect but occurs over a week or two, depending on the weather. During this time, fishing is really, really tough especially when it comes to Esox. The fish, like the water, are getting mixed up as to where their comfort zone, and its effect on their food supply. My advice if you have ventured to a lake that is in the middle of turnover, find a smaller lake to fish near by that probably has completed it, or a larger one that hasn't started yet.
Once turnover has occured, fishing generally starts to improve and will get better as time goes on. If your fishing on a Cisco based lake (bait fish), the Ciscoes start coming from deep water to rock reefs in anticipation of spawning. This brings the larger musky and northern pike that have been in deep water all summer with them. They become basically catchable at this time of year. That is one reason why fall is the big fish time of year. Fish that have been in shallower water also pull back to typically the first drop-off area near the deeper water. This happens as weeds begin to die and no longer give off the oxygen or habitat they once did. Literally, this tends to concentrate the fish from all over the lake in to predictable spots. Please don't get the idea that you can park the boat and they will jump into the boat, because that won't happen. Daily weather (wind, sunlight, temperature) can definitely effect fishing on any given day. This little discussion centers on general traits, but you still need to be aware of good green weeds, rocks, etc. It is not uncommon on a warm day, to have the big fish go shallow again. If you have green weeds (not dead ones), this can still be a fish magnet. If you have been visiting this website for sometime, the fish in the above picture was taken in October near a rock point, over green weeds, with a surface bait (top raider). Anybody that fishes in the northern U.S. or Canada typically would think a top water bait looses it effectiveness when the water temperatures fall. I would agree with that, but you have to observe your situation and be flexible. As you can see from the photo, it does pay off.
In summary, during turnover = poor fishing, after turnover start looking on breaks/drop-off or rock humps near deep water. Also, be smart enough to realize that if you aren't being ate, modify where you are looking and/or the methods that you are using.
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Last updated on ... November 30, 2002