Would You Expect a Swimming Pool and Shallow Pond to Exhibit a Thermocline?

Thermocline

• Large bodies of water, such as lakes, seas and oceans, generally contain three layers of water: the mixed layer, the thermocline and the deep water. Thermocline entails a transitional layer in which the temperature of water drops drastically. The mixed layer maintains a relatively consistent temperature similar to that of the surface of water, while the deep water maintains a consistently cold temperature because little light and heat penetrate it. Nearly all of the temperature differences between the surface of water and its deepest recesses occur in the thermocline. You can feel this transition when swimming in lakes.

Swimming Pools

• Mild thermocline can occur in standard outdoor pools. The phenomenon only occasionally affects swimming pools. Environmental factors can increase the chances of thermocline in a pool, such as a lack of natural light and heat reaching a certain area in your pool. Thermocline in a swimming pool poses no genuine danger other than the shivers, though you can decrease its likelihood by regularly circulating the water in your pool.

Ponds

• Thermocline occurs regularly in ponds, though not necessarily very small ponds such as those in your garden. Large ponds often exhibit thermocline. The likelihood of thermocline occurring increases in areas with a wide temperature range from season to season. Thermocline in ponds with organisms like plants, fish, frogs and more can cause serious damage to the ecosystem -- because most aquatic organisms only tolerate a very specific temperature range. Using aerators to circulate water can help avoid thermocline in ponds. Always consult an expert before aerating a pond with thermocline, as improper aeration can cause toxins from the deep water to penetrate the thermocline.

Additional Information

• While thermocline can occur in ponds and swimming pools, the change in temperature in these situations is never as severe as that found in lakes. In a pond or swimming pool, sunlight can penetrate all the way to the bottom, unless your pool is very, very deep. Lakes, on the other hand, allow no light penetration at their deepest point. It can prove very difficult, it not impossible, to control thermocline in a lake. Contact a local university extension to determine whether thermocline occurs in swimming pools or ponds in your area, and for advice on avoiding the phenomenon.