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.




Tell us what you think!

Possum Kingdom Lake Email Updates


 

Visit our Possum Kingdom Lake Sponsors!

Possum Kingdom Lake on Social Media

 
   

Possum Kingdom Lake Current Weather Alerts

There are no active watches, warnings or advisories.

 

Possum Kingdom Lake Weather Forecast

Friday

Mostly Cloudy

Hi: 67

Friday Night

Chance Rain

Lo: 58

Saturday

Rain Showers Likely

Hi: 63

Saturday Night

Mostly Cloudy

Lo: 50

Sunday

Mostly Cloudy

Hi: 62

Sunday Night

Partly Cloudy

Lo: 51

Monday

Mostly Cloudy

Hi: 69

Monday Night

Slight Chance Rain Showers

Lo: 58


Possum Kingdom Lake Water Level (last 30 days)


Water Level on 12/9: 993.10 (-5.90)



Possum Kingdom Lake

Fishing Report from TPWD (Dec. 7)

GOOD. Water lightly stained; 53-57 degrees; 5.89 feet below pool. Striper fishing is good in 20-40 feet of water with live bait being the key to the catch. Sand bass are on fire using chartreuse, white or pink slabs in 20-30 feet of water. Catfish are good on cut shad fished shallow in 5-15 feet of water. Water clarity is 2-4 feet of water. Report by TJ Ranft, Ranft Guide Service.

More Fishing Reports