Why Does A Lake Turn Over?




Whenever we get close to the colder months of the year, every experienced angler starts to mention the term ‘lake turnover’ more and more often. But what does it mean, and why does a lake turn over? This process usually takes place when we leave the warm summer months and the temperatures begin to drop.

Of course, these turnovers could differ from each other depending on the size of the lake and the change in temperature. For example, the water in shallow lakes tends to mix more frequently, and it does not undergo the process of stratification. But we will talk more about this in a bit.

Another common topic is that lake turnovers result in changes to the smell and taste of the water. This might sometimes be the case – we will shed some light on these changes and how they could affect the lake’s inhabitants. But before we get to this part, let’s go into a bit more detail on the topic of ‘Why does a lake flip?’


What Causes Lakes to Turn Over?

As we already mentioned, lakes flip when the weather gets colder. But why does this happen? Simply put, the water in stratified lakes can be split into three layers:

  • The upper layer is called the epilimnion. During the warmer months, this layer has a noticeably higher temperature.
  • The middle layer is known as the thermocline. This layer sits between the epilimnion and the hypolimnion. It has a very steep temperature gradient.
  • The bottom layer is called the hypolimnion. This is the colder layer of lake water.

Now that this is out of the way, it is time to mention water density. When the temperature of water changes, it also changes its density – hence why its weight fluctuates. According to the U.S. Geological Survey (USGS), water is densest at a temperature of 39.2°F or 4.0°C. So, what does this mean in the context of a lake turning over? When the temperatures drop, the top layer of water starts to get colder as well. It inevitably reaches a point in which it becomes denser than the water underneath, therefore causing it to sink. During this process, the bottom layer of water starts shifting to the top – hence the term turning over.

As we already mentioned, this process may happen more than once a year. But, typically, summer lake turnover is the most common scenario. It is important to add that not all lakes are stratified. Shallow lakes rarely have their water separate in layers with different temperatures, hence why they are more unlikely to turnover.

Lakes are also classified into several categories, depending on how often they turn over. There are four general categories, though:

  • Cold monomictic – the water in these lakes does not go over 39.2°F, so lake turnover occurs once during the summer months. For example, most lakes in the Arctic are cold monomictic.
  • Warm monomictic – a common type of lake whose water usually reaches the 39.2°F mark during the winter, and they experience turnover during this time – such as the major lakes in the South.
  • Polymictic – they frequently mix throughout the year. An example of this is Lake Waco.
  • Dimictic – the water in these lakes stratifies during the summer and winter, and they usually experience turnover twice – once in spring and once in fall.

Does a Lake Flip Affect Taste and Smell?

Many people report a noticeable change in the smell and taste of water when this happens. However, the lake turning offer might not always be the cause of this event – there might be other factors at play.  

One of the common reasons for lake turnover smell is the fact that the algae bloom during this process. And if you do not know why this happens, then we have a brief explanation. During the warm summer months, the lake’s water stratifies – as we already established. Because of this, the bottom layer of water (or the hypolimnion) tends to get de-oxygenated – new oxygen cannot reach it. But that’s not everything – the hypolimnion also becomes the home to everything that sinks to the bottom during these months. This includes dead algae, dead weeds/leaves, and more. The common thing between all of these is that they release phosphorus while decaying – the primary fuel of algae. As you can probably already guess, when a lake turnover happens, all the phosphorus-rich water gets to the surface and gives the algae there enough fuel to bloom.

Lake turnover smell could also be caused by water treatment amenities – such as ozone. Thanks to this type of treatment, the bacteria, viruses, and metals in water can be eliminated. This, in turn, could slightly alter the smell and taste of the water. This change might also be more noticeable during the different months of the year since water usage tends to fluctuate. For instance, in the winter less water gets used, which means that it sits stagnant in supply pipes for longer than in the summer months.


How Does a Summer Lake Turnover Affect Fishing?

Lake turnover is essential for a healthy environment in lakes that experience stratification. The mix of the different layers of water ensures that oxygen is replenished regularly, and the viable habitat does not decline. If a lake turnover does not occur in a stratified lake, this could lead to the partition of hypoxic zones or dead zones – where oxygen is at a minimal level.

Although many fishermen tend to abandon their favorite hobby temporarily when lake turnover season comes, you should know that fishing during this period is not out of the question. While the waters tend to get a bit muddy, fish is still out there for the taking. However, you might want to switch up your tactics a bit. Because of the water mixing that occurred recently, the viable habitat for most species has been broadened – this means that you want to use versatile bait, which is ideal for both shallow and deep water.

Another factor that plays a role is that lake turnover often serves as a motivator for fish to feed – since it is a sign that winter is approaching.

One fishing tip is to find the temperature thermocline, and often you’ll find fish, especially during the summer months when they are seeking the coolest water that still has decent oxygen saturation. Once you locate where the fish are suspended in the water column, then you’ll know exactly what depth to fish at, and increase your chance of success out on the water.




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Fishing Report from TPWD (Sep. 21)

EXCELLENT. Water stained; 80 degrees; 1.70 feet below. Striped bass are good scattered from shallow flats to deeper water biting on slabs. Some topwater action early in the morning, and midday. Sand bass are mixed in with the stripers on shallow flats. Report by John Blasingame, Adventure Texoma Outdoors. Striped bass are great on live shad fishing main lake flats and secondary ledges in 30-40 feet of water. A lot of smaller fish with the occasional big fish, the size will improve as the weather cools off. Largemouth and smallmouth bass are slow with the amount of shad in the lake making it tough to fool them. Still off the banks in 8-15 feet of water fishing soft plastics late in the day and topwaters the first couple hours of the day. Key in on underwater points and brush piles using electronics. Blue and channel catfish are great on flats in 20-30 feet of water moving shallower as the water temperature cools off using cut shad and prepared baits. Trophy blue catfish season is just around the corner. Crappie are mostly undersized with better fish mixed in as you move around. Target roaming fish with electronics fishing the tops of brush piles in 10-15 feet of water. Minnows mainly and a jig if you get them biting well. Report by Jacob Orr Lake Texoma Guaranteed Guide Service.

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