It would have to be a pretty hard and long frost to freeze a decent fish pond solid in this country.
As you say water is most dense at 4C, so it sinks to the bottom of the pond. As the surface of the pond gets colder it gets *less* dense and floats on the 4C water below. Convection stops and the only way the lower water is going to freeze is by conduction, ice is a pretty poor conductor of heat and the lower levels are in the relatively warm ground as well.
"All science is either physics or stamp collecting" (Ernest Rutherford; I think nowadays we'd say maths or stamp collecting given much of modern physics).
But in a different thread, snipped-for-privacy@aol.com has recently written
which discusses this and 40 other interesting properties of water.
Douglas de Lacey
I thank you for that link, it brought back a few memories.
I used to work in the Fire Brigade and, as you would expect, water plays a major part in their activities. During lectures I often asked my class "why cold water could be lifted (sooked up) from a greater lift than warmer water" and "if heat rises, why does ice form on the surface of a pond and not at the bottom".
This link explained it technically but would go over the head of most of the students. The samples were only used as a point of interest.
Sorry for going OT a bit
Bill
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