Turnover refers to the exchange of surface and bottom water in a lake or pond. This annual recycling program happens twice a year. There's spring turnover and fall turnover and summer stagnation in between. From spring to fall, warmer water goes from the top of the lake to the bottom and cooler water moves from the bottom to the top.
An understanding of turnover, combined with knowledge of what kind of water a particular fish likes, can make you a real fishing genius. As always, good luck.
Once the ice is out, the water on the surface of a lake starts to warm. When it reaches 39 degrees it begins to sink and is replaced by cooler water from below. This exchange continues until the water temperature is constant in the entire lake. Early in this process, fish will stay in the shallow areas of the lake where the water warms up faster, and where the first plant growth of the spring occurs.
During the summer, the sun heats water near the surface of lakes, but it doesn't sink. Eventually a condition known as "stratification" develops, putting a well-defined warm layer of water over a cool one.
Fish like the cooler water, but they also need the higher oxygen levels found in warmer water. So they'll migrate to an area right between the two levels of water called the thermo cline. The thermo cline can occur between 2 and 10 feet in depth, depending on the size of the lake.
It's best to find a point or some other form of structure that extends out from the shoreline and slopes gradually down into the thermo cline. This should be a place where fish can find warmer water, but have quick access to deeper, cooler and safer water.
With the arrival of fall and cooler air temperatures, water at the surface of lakes cools, becoming almost as heavy as the cooler bottom water. Strong autumn winds move surface water around, which promotes mixing with deeper water. This is fall turnover.
As mixing continues, lake water becomes more uniform in temperature and oxygen level, allowing fish to move around freely. Fish can be difficult to find as long as these conditions prevail, usually continues until the weather turns cold, chilling the lake's surface.
Water Temperature and Turnover
Each fish has a different range of water temperature in which it can survive. Although fish cannot always find the exact temperature they prefer, they are usually found in water close to that temperature.
By combining a knowledge of preferred water temperature and lake turnover, you can kind-of-sort-of predict which fish will be in a particular part of a lake at a particular time of the year.
Fish that like warmer water will be surface feeders in the summer and bottom feeders in the fall. And fish that like cooler water will feed deep in the spring and on the surface in the fall. But don't hold us to this. Fish are always tough to catch.
Too many hot days in the summer can make fish in shallow lakes, ponds and rivers sluggish. The same thing happens in the winter when water temperatures are lower. Why? All fish are cold-blooded. Meaning they can't keep their body temperature at a constant level like humans and other warm-blooded animals. So the temperature of their surroundings influences the fish's body temperature and bodily functions. Really high and really low water temperatures reduce the amount of oxygen in the water, making fish less active and picky about when and what they.
So here's the first rule of when to fish. Fishing will be slower when it's too hot or too cold.
Understanding this bit of biology will help you decide what kinds of lures and baits to use, and how fast or slow to work them. Work your tackle slower in colder water and faster in warm water.
Fish prefer early morning and evening sun to the bright sun of midday. Morning sun warms the shallows, creating more comfortable water temperatures for fish to feed. Late morning is best when the sun has had more of a chance to warm the shallows. This is particularly true during early spring in shallows with dark or mud bottoms because dark areas absorb heat more rapidly than light sandy bottoms.
Warm water temperatures make bait fish more active and available to game fish on cool early-spring days. On hot sunny days, fish move to cooler, deeper waters to stay comfortable. High-heat conditions make shallow and top water lures and bait best only in the early morning and late afternoon when cooler temperatures and lower light levels allow fish to cruise the shallows for meals.
In midday, hot water surface temperature, decreased surface oxygen and occasional increasing winds cause fish to move deeper. In these conditions, deep fishing baits, rigs and lures are best.
Already, you can see how a combination of time of day, light and weather can affect your fishing.
Variable Weather Conditions
Wind can play a large role in fishing success. Wind pushes water and surface food to the far shore, with bait fish behind it, and with game fish behind the bait fish. So if you're fishing from shore on a windy day, fish where you have to cast into the wind. That way your lure moves with the wind, just like the other food in the lake at the same time. If you're fishing from a boat, cast with the wind on a sheltered shore.
Storms and changing weather patterns affect fishing success since fish are keenly attuned to changes in barometric conditions. With many fish, feeding increases during the hours immediately before a cold front, but slows during and after a storm or front hits.
Fishing after a cold front is poor and continues to be poor for a day or two. Warm fronts cause surface water temperatures to increase, putting fish into a feeding mode. This can be particularly true in the winter, when a warming trend can cause otherwise sluggish fish to start feeding actively. Most of this feeding activity is on or near the warm surface.
Cloudy days improve fishing since the clouds prevent light penetration. Overcast skies cause fish to cruise for food more than they would during bright days when they tend to hide and stay close to structure. On overcast, cloudy days, fish are less likely to be at specific structure spots or areas and more likely to be scattered throughout a waterway.
A light rain is another good time to fish, especially a warm spring or summer rain. Rain can help you hide from the fish since the rain breaks up the view a fish has through the water surface. This is true for shore, wade or boat fishing. Rain also washes insects and bait into the water, creating a feeding binge for fish.
Hard rain conditions are a poor time to fish. A hard rain muddies the water, makes it difficult for fish to find bait or lures and causes heavy runoff, which can clog their gills. The increased water flow in rivers from any rain increases current flow and makes it difficult for fish to maintain a comfortable position in the river. High water levels can also create rapids, waves and unsafe fishing conditions.
When there's lightning or the possibility of lightning, get out of the water immediately, whether you're in a boat, wading or on shore. Safety first. Plus, there's no way you're going to catch fish in a violent storm.