The oxygen level of the water drops for a short time as the oxygen-depleted hypolimnion mixes with the water above. The water continues to cool as it circulates, aided by wind. TURNOVER: The thermocline disintegrates, and water mixes from surface to bottom.

IMMINENT TURNOVER: The thermocline shrinks as it approaches the same temperature as the uniform mass of water above. During the summer, the surface temperature of the water in temperate lakes is warm. After the ice leaves in the spring the water is fairly uniform. Waters density reaches its maximum at 4 degrees Celsius, as you may know. Oxygen-poor water remains trapped below the thermocline. Temperature and Dissolved Oxygen (DO) profiles give us important information about the lake.

The thermocline remains intact but becomes closer in temperature to the layer above. POSTSUMMER: The surface of the water radiates heat to the atmosphere at night as water above the thermocline gradually cools. The lower (coldwater) level usually contains less dissolved oxygen than the upper layer. 2007), global lake surface temperatures have also increased substantially (OReilly et al. SUMMER: The upper (warmwater) layer may be from 12 to 40 feet thick, while the thermocline may be 2 to 15 feet thick. As atmospheric temperatures have risen in recent decades (e.g., Trenberth et al. Once the lake or reservoir has turned over, the fall Coldwater Period begins. As cooled water from the surface sinks to the bottom, debris bubbles up to the surface, accompanied by hydrogen sulfide and other gases produced by disintegrating plants, releasing a musky or sulfurous smell.įishing gets difficult under such conditions, but fortunately, Turnover lasts only about a week on any one lake. Wind encourages the mixing, and eventually the thermocline narrows, then disappears. Some of our favorite lures for this process are football jigs, tube jigs, or ned rigs, oftentimes utilizing a craw or minnow-colored soft plastic.As cold weather rolls in from the North, the surfaces of reservoirs and lakes cool, making their water heavy enough to sink and mix with cooler water in the thermocline below. If possible, fan cast to cover all of the water in the area in search of your target species. The second process is to go to an area that you know fish were abundant in throughout the summer and slow down and fish that entire area very methodically. Remember to clear your trolling lines often because of the extra debris in the water. It is caused by water temperatures being different at the. Some lures to keep in mind during this period are typical trolling lures such as spinners and spoons or casting and retrieve lures such as swim jigs, topwater lures, and crankbaits. Lake turn over is a phenomenon that generally occurs twice a year, spring and fall. The more water you can cover, the more fish you will encounter. Fish are generally scattered throughout the lake, shallow to deep and on-shore to off-shore. The first process is to cover as much water as possible. There are two schools of thought to catching fish during this period. During the autumn when water temperature drops to about 4 degrees C, BC coastal lakes thermally destratify and thus lake water can mix throughout the winter. The lake turnover period can be challenging to fish, but keep in mind that fish are still present and they still need to eat. Some will suspend and roam, others will hold tight to cover in ambush. Fish during this period can move around a lot! Some fish will move very shallow, while others will retreat to deeper water. What this means for anglers… There will no longer be a stable, highly oxygenated section of water in the water column, and the reliable Summer patterns you’ve been fishing will disappear. This debris can make it troublesome to troll through, with build-up on your trolling lines.Īfter a lake turns, it can take 2 to 3 weeks for the lake to re-stabilize. Also, the rising warmer water will bring algae and other debris from the bottom of the lake.

Fall and spring turnover are natural phenomenon that cause the top layer of the lake (the epilimnion) and the bottom layer of the lake (the hypolimnion) to trade places. This shift to the overall water column is called lake turnover.Īfter the lake turns, the water temp will be relatively the same from top to bottom, and the dissolved oxygen levels will be relatively the same from top to bottom. Field Notes Janu4 ways to describe turnover, and how it helps our lakes Read Time: 3 mins What causes lake turnover Turnover is like a dog learning to roll over. At a certain point, the surface water reaches a lower temperature than the water below, and with the cooler water being denser than warm water, the surface water suddenly sinks to the bottom of the lake. In the Fall, water temps on lakes and reservoirs begin cool at the surface.

Lake turnover water temperature