~ jan wrote:

Check my reasoning.... So the reason slow flow movement in a pond keeps an
area liquid is, 1) because it isn't pure,

No. If the water is actually below 0C, it's going to freeze. Whether or not
it's moving will make no difference.

and 2) it is keeping the temp mixed?

Pretty much - the water in contact with the ground at the bottom of the pond
is going to be warmest (if it gets cold enough that the frost reaches that
far, it will _still_ be warmest, because it's going to be darn cold at the
surface!), so moving it is essentially speeding up the transfer of heat
from the ground throughout the pond. It's also speeding up the transfer of
heat from the water to the air - but if your pond is mostly frozen, that
heat transfer will be much slower than the transfer from the ground.

--
derek