When scuba diving (especially in the Great Lakes) you can sometimes "see" a thermocline. Obviously I'm not talking submarine depths here but rather 35 feet or 60 feet or more depending on the conditions. It's hard to describe but it's kinda like a shimmery "current" and is one of those things that you see better if you don't look right at it (underwater "northern lights", LOL). There is also a noticeable change in temperature.
I suppose if you poured hot water into a large tub of cold water you'd briefly see the effect I'm trying vainly to describe.
