What Happens When a Lake Turns Over
In last weeks column, we talked about that “sweet spot” on our lakes, the thermocline. To refresh, the thermocline separates the warmer oxygen-rich layer of water separated from colder oxygen-deleted water below the thermocline.
There is another feature on lakes in later summer that upsets the balance of the water above the thermocline and that below this line. It’s called “stratification” or as we know it best, when a lake turns over.
I had to do some research to find out just what this phenomenon is, how it works, when it happens and the effect on the lake and its fishery.
As autumn air temperatures decrease, the surface water of the lake begins to cool, causing the density of the water to increase. This denser, cooled water starts to sink, displacing the slightly warmer, less dense water below. This continuous sinking and displacement gradually deepens the thermocline, pushing it deeper and weakening the stratification barrier.
As the surface water warms, it begins to sink until the entire water column reaches a uniform temperature. Wind and currents work together to mix the lake completely.
When it mixes completely, the oxygen-rich surface layer is rapidly moved down, replenishing the oxygen supply for deep water organisms. Simultaneously, the nutrient rich water that had accumulated at the bottom is brought to the surface. This bottom water typically contains high concentrations of nutrients, such as phosphorus and nitrogen, which are released from the sediments in low-oxygen conditions.
This sudden upwelling of nutrients to the sunlit surface layer can fuel rapid growth of plankton and algae.
How can the average observer note that the water has turned over? There will be a noticeable change in water color and odor; you can actually smell an unpleasant odor from all the stinky stuff that had been on the bottom layer such as the release of dissolved gases like hydrogen sulfide and methane that is now on the surface. You’ll also notice more algae blooms.
Surface water takes on a turbid appearance, not clear or transparent because of the stirred-up sediment and mud creating a temporary unpleasant odor.
Anglers often stay off the lake when a turnover occurs because of the stinky off-colored water. The fish may not be in the same areas they were before this happens because water temperatures and oxygen won’t be confined to the top layer now that the oxygen depleted lower area had mixed with the top. They could be anywhere, shallow to deep when this occurs. This makes fish concentrations harder to predict and can be a problem as you have to search harder to find fish which are more likely to be scattered rather than being concentrated together in one particular spot.
We are reminded that a lake is not simply a single body of water. It is a living, layered system always changing with the seasons.
I find this most interesting when we realize that our favorite lake has a mind of its on and can do some interesting things, especially when it turns over.
FISHING REPORT
CANEY LAKE – Bass are fair around the grass early on topwaters. Later they’re around deep drops. Soft plastics and cranks baits are working fair. Crappie are around the deeper tops and are hitting jigs and shiners. Bream are slow to fair. For information contact Caney Lake Landing at 259-6649, Hooks Marina at 249-2347, Terzia Tackle at 278-4498 or the Honey Hole Tackle Shop at 323-8707.
BUSSEY BRAKE – Crappie are deep and are fair on shiners or jigs. Some bass are being caught early on topwaters and later by flipping the trees and lily pads with oversized soft plastics. Fishing overall has slowed because of water temps being so warm. For latest information, contact the Honey Hole Tackle Shop at 323-8707.
OUACHITA RIVER – Bass are fair on crank baits and soft plastics. Crappie are fair in the river lakes. For latest information, contact the Honey Hole Tackle Shop at 323-8707.
LAKE D’ARBONNE – Bass are overall slow but best on topwaters early and crank baits and soft plastics later on secondary points. Crappie are in deep water in the channel and fair on jigs and shiners. The bream have slowed now that the water and air temperature has warmed. Catfish are fair on red wigglers and night crawlers fished just off the banks. For latest information, call Anderson Sport Center at 368-9669 or Honey Hole Tackle Shop at 323-8707.
LAKE CLAIBORNE – Crappie are suspended where there is more oxygen. Bass are in the shallows early hitting topwaters and in deeper water around around the channel edges later. Soft plastics and crank baits are picking up a few. Night fishing is best now that the weather is turning hot. Bream are slow. For latest information, call Kel’s Cove at 927-2264 or Terzia Tackle at 278-4498.
LAKE YUCATAN – The water level is falling. Catfish are being caught on trotlines and buffalo caught in nets. Crappie and bass have not started to hit. For info call Surplus City Landing at 318/467-2259.