Cold weather, especially cold nights, change everything for our fisheries. That doesn’t mean fish won’t bite or be shallow, but they can indeed be fickle creatures to pattern this time of year.
As we get nighttime temperatures into the 30s, the mix of warm water near the surface cools rapidly and settles as cooler water to the bottom. The epilimnion, top layer, turns over to the hypolimnion, bottom layer, and the upper layer becomes denser and sinks. The lower level can rise when the top levels fall.
That mixing means the turnover has begun and honestly it doesn’t take long to occur, normally two or three days. Typically it can be recognized with color of the water, but the smell can be different too. Gunk from the bottom can be seen floating on the surface as the heavier cold water begins to appear throughout the water column. Turnover can be a very hard time to fish until the fish get acclimated to their new temperatures.
Turnover does not occur on all lakes and those with current or a lot of wind will not. Still lakes and those that are void of current will. There is no thermocline. The most comfortable area for fish is gone during this time so it takes a while for fish to get used to the new environment.
Some will stay active the entire time and fish can still be found both deep and shallow during this time of year. Because it can take a day or two for them to get used to it, they might bite even better when they do. Depth changes the variables of when and how fast this will occur.
Here in Central Illinois our lakes are considered shallow and as a result turnover isn’t as dramatic, but it still impacts the fish. Generally, because fish are cold-blooded, it doesn’t take long for them to get used to the cooler temperatures and they have to eat. It’s maybe not as much as they do in warmer water as their metabolism slows down significantly. Digestion of what they eat is slower too, so they may not eat as often.
Oxygen levels during turnover can be wickedly low where it is mixing. Fish may suspend and you will see shad and gamefish in an area just above the area it is mixing. Upper ends of the lake are usually the first to be impacted as they are shallower.
A good rule of thumb is to stay ahead of the “dead areas” and move a bit out of pockets or to the area where the creek becomes the lake first. Heavy rain or wind can flush out the turnover more quickly. As it ends, the water will clear and that is a great starting location to get a bite or two.
A myth about turnover is that fish will not chase a bait or prey during this time. Fish that are suspending are tougher to catch, but starting shallow and banging into the cover with crankbaits, spinnerbaits, jigs and plastics can activate the bite. I know of no better time to be throwing a squarebill than now.
Depending on water color, color choices will vary but clearer water means shad patterns and chrome where in muddy water chartreuse and black/yellow are best bets. They will chase and paralleling the bank is optimum in the fall, especially when rip rap and blowdowns are present. Having deeper water nearby is an added plus.
The sun is your friend in the fall and cold fronts are less impactful after the turnover. Some of my best days in the fall were calm, cold days with bluebird skies. Most anglers hate those days, but the fish do not recognize it and unless a severe high pressure system is over you fishing can be excellent.
I call this time of year “rope and winch” time and I always have heavy line, a stout rod and big baits with large profiles available. Dense, heavy cover is a great place to start and after a bite or two you will find the depth the fish are holding.
Bundle up, bring gloves and wear heavy socks and don’t be afraid to brave the elements as autumn can be gangbusters. Know the signs of turnover and figure out the best way to beat the variables. You may not get a lot of bites, but I would bet that other than during the spawn more big fish can be caught. You will never know sitting on the couch.