Posts: 149
| Generally in northern Wisconsin turnover occurs in the low 50's, say 53 degrees or so. Keep in mind that water is the most dense it can be at 39 degrees F. As the surface water cools in the fall, it will cool to the point of being more dense than the cooler water which was at the bottom of the lake all summer (which was somewhere in the 50 - 55 degree range) , thus the cooled surface water sinks and mixes with the bottom water layer. Now all water in the lake is the same temp and 'turnover' is complete. This will continue to be the case (all water in the lake the same temp) until the water is 39 degrees, at which point water that is cooled to a temp below 39 will stay as the top layer and eventually cool enough to form ice. All winter long the warmest water in the lake will be 39 degrees right at the bottom. In spring a mini 'turnover' will occur as the ice disappears and the surface water warms to a temp higher than 39 (usually a day or two after ice out) which will once again cause the top layer of water to mix with the bottom layer and 'turnover'. This spring 'turnover' is hardly noticable, as the temp difference between the top and bottom of the lake isn't as great in spring as it is in fall. The cooler water will then stay at the bottom all summer until the surface cools to that temp in the fall, starting the cycle all over again.
As for visual signs, if the water is very turbid and the temp is in the low to mid 50's, you're right smack in the middle of turnover. If the water is lower than the low to mid 50's and somewhat clear, then turnover is complete. One sure way to tell is to take temp readings all the way through the water column. If they are all nearly the same, then turnover is complete. |
