One thing I never realised is how dramatically the viscosity of water changes with temperature. This is probably why you can recognise hot water from a cold water in a video.
Temperature (C) / Viscosity (mPa*s)
0.01 1.7911
10 1.3059
20 1.0016
25 0.89002
30 0.79722
40 0.65273
50 0.54652
60 0.46603
70 0.40355
80 0.35405
90 0.31417
99.606 0.28275
Therefore, between 0 and 4°C the usual law of natural convection (heat rises) is inverted and you get "heat falls" instead.
What this means is that in winter, the ice on top of water can be frozen but the water can be warmer further down and resist further heat transfer. Natural convection will not act to cool the water from above, and a stable stratified temperature gradient can form. This allows bodies of water to remain liquid in winter for longer than you'd expect in a "normal" liquid.