Why in super cold weather, only the top layer of the pond water freezes? and to add on, the fish do not die?

need help to answer this in chemical terms, chemical bonding etc. Help is greaty appreciated,, i nid the answer urgently THX!Why in super cold weather, only the top layer of the pond water freezes? and to add on, the fish do not die?
The whole pond will freeze solid if it is cold enough for long enough. But the reason the top freezes first is because water is densest at four degrees. As it gets colder than four degrees it exspands, so the coldest water rises to the tops and freezes. This is because of they hydrogen bonds in the water molecules.





The fish can live until the oxygen runs out. But snce cold water can have more disolved gasses than warm water it can take a while.Why in super cold weather, only the top layer of the pond water freezes? and to add on, the fish do not die?
When water freezes it forms a crystalline material called ice. The molecular structure of ice places the molecules in an orderly pattern. This pattern has a lower specific gravity than liquid water. Less dense materials are displace by higher density so ice floats. The ice layer on top of a pond insulates the water underneath. The fish who live in the water can survive until spring.
Water is unusual in that its solid form (ice) has a less dense structure than the liquid. That's due to the very specific 3-dimensional array of hydrogen bonds that holds water molecules together in the solid state. Because ice is less dense than water, it floats. When water freezes, the ice forms on the top first, and instead of sinking (as most frozen liquids would do), it stays on the top, forming an insulating layer that protects the rest of the water from the cold. Given enough time and enough cold weather, the water beneath will gradually freeze, but not nearly as fast as would happen if the ice sank as it formed, exposing a new liquid surface to the cold air. Hence lakes and ponds stay mostly liquid throughout the winter, and the fish can keep on doing what fish do.
Oxygen is still in the water even though you do not see it , and passes through the fish's gill,s to allow them to breath while swimming.


Also, Moving water does not freeze with fish moving below keeps water circulating even though top remains still which will freeze as temp is cooler at the top then at the bottom


But beware! If no air hole // breathing hole !!on top for air to get back into water fish will soon suffocate as needs regular supply of air to breath.


Unless a natural pond, which most have under ground springs which constantly feeds new water and oxygen in to the pond below does not freeze and water slowly gets absorbed back into the ground.


the water in the bottom of the pond is warmer then the top of the pond , also depending on which type of pond you were talking about plastic ponds for koi or natural pond that has frog's, sun fish etc.they also go into a type of hibernating state and their functions slow down a lot but still move around .
check this site out. for ';only the top layer of the pond water freezes'; if you want more chem terms





and for the fishes.


Plants and animals can live under ice because of water's unusual quality of being most dense at 4 degrees C. Ice has a density about 93% of water so it floats on top. Water is most dense at 4掳C. Deeper water below the ice stays at 4掳C because colder water rises to the top due to its lower density. So at the bottom of a frozen lake, stream or pond, it's always 4掳C, warm enough for life-or hibernation at least.