Lake Monona dive 10/12/10

[rk_diver]

Found two more sunken boats last weekend, dove on one last night. Registration expired in 1978 (same year as the last one I dove on, must have been a bad year!), it's a 15' fiberglass. Water clarity was terrible, all the way down to 55'. Historically below the thermocline it clears up nicely, but in Monona depth is meaningless, it's crappy throughout the thermocline. For the first time I don't even remember feeling the thermocline when I descended, I had to check the dive computer later to see if there was even one. There was, minimum temp was 55°F (surface temp was 66°F). Rick

[D.W.]

Rick,
Always love reading your posts. A couple of questions in an effort to understand more about the thermcline. Is 10° difference from min to surface the norm? I would have guessed it to be more. What depth does the thermocline set on Mononna? Has turnover happened? Is it clear below the cline at other times of the year on Mononna? Thanks again for sharing your view from below. Later D.W.

[rk_diver]

D.W., Typically the temp below the thermocline is 55°F to 57°F, so the temp difference depends on warm the surface water gets in the summer. Right now it's cooling off so there's less of a difference. Again, typically the thermocline is at 30' in the summer. As fall approaches and water temps cool the thermocline will get deeper and deeper. With the 55 to 57°F typical temp in mind turnover starts when the entire water column is the same temp, then some good strong wind will mix the water column and everything flips over. This re-oxygenates the entire water column, allow life to exist at every depth. Usually below the thermocline, in our lakes, it's pitch black since no sunlight penetrates trhough the thick algae in the upper water column. There's also little living algae below the thermocline, so traditionally the water clarity is gratly improved. Monona is no longer typical though, it has thick algae and other particulates throughout the entire water column. So, turnover will start when the upper water column cools to 57°F. Cooler water is more dense then warm water, with it's greatest density at 19°F. Lower then this it becomes less dense and rises back up to the surface. That's why ice floats. Hope this helps! Rick

[Rocky1]

Rick, thanks for the info. I was on Mendota Tuesday and water was very green with dead grass floating on top in several places. It sure looked to be in the turnover stage to me. Below are the water temps from GAMIS site for Mendota.
Surface to 45'+ are almost the same..thanks

Water Temperature
Surface 17.1°C (62.8°F)
-1m 17.3°C (63.1°F)
-5m 17.4°C (63.4°F)
-10m 17.4°C (63.2°F)
-15m 17.5°C (63.6°F)
-20m 12.3°C (54.2°F)

[Muskie Nut]

Rick did not answer one of your question directly. Turnover has not happened yet as of today, October 17th. The surface is too much warmer than the lower depths.