Question

why did not freeze water at lowest palace in pond..or rivers in winters

Answer 1

because in all river and pond are not much live freeze

Answer 2

The specific heat capacity of water is higher than most of the liquid. So freezing or heating water takes a lot of energy to be absorbed or put into the liquid that is water so freezing of heating the whole water body can take or give out a lot of energy which actually doesn't happen so only the upper layer of the water body is heated or cooled.

Hence only the thin layer of water on the top is freezed and it turns to Ice while the rest remains liquid. This is also sometines called anomalous expansion of water.