When humans get hot from the heat of summer, we get a cold drink and fine a cool room or if we are out on the lake fishing, we take along some cold water and a cool head covering and continue to fish as best we can in the heat. The fish in reservoirs also seek a cool and comfortable spot but unfortunately for the fish in Lake Oconee and Sinclair finding a good cool spot with plenty of oxygen is tough during the summer months.
Some of the inability to find a cool spot, results from the fact that those reservoirs do not have multiple layers of water like other lakes. The reason for that is due to the pump-back operation at the Wallace Dam. The water in a normal lake or reservoir during the summer will separate into distinct layers but that does not happen in Lake Sinclair and Lake Oconee.
In normal reservoirs, the water column stratifies and breaks into differ temperatures at differ depths and so does the oxygen content in the water. A layer of water called thermocline develops between a layer called epilimnion and a layer called hypolimnion. The thermocline layer contains cooler and good amounts of dissolved oxygen where the fish can thrive during the heat of summer.
Angling success in those lakes can be great even during the hottest weather. Anglers just have to locate the thermocline in those lakes to be successful. In those normal lakes, the upper layer above the thermocline or the epilimnion also contains good oxygen levels but is the hottest water in the lake. The lower layer or the hypolimnion below the thermocline is cooler but has little to no oxygen.
But on Lakes Oconee and Sinclair, we see little or no stratification during the heat of summer and little or no thermocline will develop. The water temperature and oxygen levels are basically the same from top to bottom but there is slightly more dissolved oxygen at or near the lake’s surface. That makes for tough angling during the summer months.
Dissolved oxygen is a measure representing the amount of oxygen in the water. Most dissolved oxygen comes from the atmosphere but it can be depleted by high water temperatures. Dissolved oxygen can also be increased by rain and wind. Fish need dissolved oxygen to survive.
Most fish species can adapt to low dissolved oxygen levels but when dissolved oxygen in the water drops to 5 mg/l or below, the fish are under stress. Fish can survive and adapt to levels as low as 2-3 mg/l for short periods but below that level, the fish will begin to die.
As the summer weather takes hold on Lakes Oconee and Sinclair, the water temperatures rises and dissolved oxygen levels steadily drop. The pump-back operation at the Wallace Dam on Lake Oconee and to a lesser degree the coal fired power plant on Lake Sinclair does not allow either lake to stratify like other reservoirs. The water is continually mixed from top to bottom by the pump-back operation.
In normal lakes, the thermocline is easy to find and that is where most of the fish in the lake will reside for the majority of the daytime hours during summer. Without a thermocline as is the case with Lakes Oconee and Sinclair, the fish can be just about anywhere in the water column and that makes for some tough fishing.
If the water temperature and dissolved oxygen levels were measured right now on Lakes Sinclair and Oconee, those measurements would indicate that fish are under stress and those measurements would also show that few areas of either lake have good combinations of acceptable water temperature and dissolved oxygen.
Anglers can consider some other factors that might impact where the fish are located and it might improve their chances for angling success. Weather conditions like clouds (fish will move shallow due to less sunlight) and wind/rain (creates higher oxygen levels in shallow water) can change the location of the fish on any given day and can improve fishing.
Angling success can also be better at night during the summer. Several factors come into play as daylight turns into darkness. The two primary factors are that the bright sunlight is no longer a limiting factor for the fish and the cooler nighttime temperatures might cool the shallow water by several degrees. Those factors result in the fish being more likely to move into shallow areas to feed at night.
With the pending shutdown of Plant Branch, I am often asked about the impact of the shutdown on angling in Lake Sinclair. The hot water discharge from the generation at Plant Branch has a negative impact during the summer months on the fish in Beaverdam Creek and areas adjacent to that Creek where hot water is discharged.
Dissolved oxygen levels suffer greatly during summer in those areas impacted by the hot water discharge. Once Plant Branch is shutdown, dissolved oxygen levels will improve in those areas close to the plant. However both lakes will continue to be negatively impacted during the summer months by the generation at the Wallace Dam and that negative impact is far greater on summer fishing. Good fishing and see you next week.