Name: Elkhart Lake
Waterbody ID (WBIC): 59300
Area 292 ACRES
Maximum Depth: 119 feet
Mean Depth: 46 FEET
Bottom: 42% sand, 43% gravel, 0% rock, 15% muck
Waterbody Type: Lake
Hydrologic Lake Type: SPRING
Latitude, Longitude 43.82623130, -88.02509430
Elkhart Lake helps take care of itself by doing semi-annual “flips.” With a maximum depth of 119 ft., and 292 acres, Elkhart Lake goes through a change of life twice a year. The process, which takes place in both spring and fall, is called Turnover. It is possible to actually see this process in the spring turn, when the winter ice suddenly sinks! Here is what is happening when you think the lake is just “there.”
What is meant by “lake turnover”? How and why do lakes do this in autumn and spring?
- The key to this question is how water density varies with water temperature. Water is most dense (heaviest) at 39 degrees F (four degrees C) and as temperature increases or decreases from 39 degrees F, it becomes increasingly less dense (lighter). In summer and winter, lakes are maintained by climate in what is called a stratified condition. Less dense water is at the surface and more dense water is near the bottom.
- During late summer and autumn, air temperatures cool the surface water causing its density to increase. The heavier water sinks, forcing the lighter, less dense water to the surface. This continues until the water temperature at all depths reaches approximately 39 degrees F. Because there is very little difference in density at this stage, the waters are easily mixed by the wind. The sinking action and mixing of the water by the wind results in the exchange of surface and bottom waters, which is called turnover.
- During spring, the process reverses itself. This time ice melts, and surface waters warm and sink until the water temperature at all depths reaches approximately 39 degrees F. The sinking combined with wind mixing causes spring “turnover.”
- This describes the general principle; however, other factors (including climate and lake depth variations) can cause certain lakes to act differently.
During summer and winter, the lake is fully stratified:
- Epilimnion – the upper layer is where the warm water resides.
- Thermocline/Metilimnion – mild temp but great to jump in summer and cool down.
- Hypolimnion – the lower strata where the heavier, colder water hangs out.
This turnover cycle helps the lake renew itself. So, enjoy thinking about this process as you watch the seasons change and when you go from swimming to snowshoeing on wonderful Elkhart Lake.
Keeping the lake in good shape is a major part of what the Elkhart Lake Improvement Association is dedicated to doing. Each year, ELIA works with the staff at the DNR, professional marine biologists, and with volunteers to help make “Keep Elkhart Blue” a reality for all to enjoy.
A more detailed description of the physical characteristics of lakes, including temporal and density interactions, can be found at the Water on the Web site, sponsored by the U of M – Duluth and funded by the National Science Foundation. http://www.waterontheweb.org/under/lakeecology/05_stratification.htm