Can anyone explain in short that how Anomalous expansion of water helps in preserving the aquatic life during cold weather??

Normal behavior for a liquid is to expand on heating and contract on cooling. A liquid that contracts is said to become more dense.
Water behaves like a normal liquid when it's cooled down to 4 deg i.e it contracts, but when cooled further down from 4deg to 0 deg it behaves anomolusly i.e it expands instead of contracting further. So ice at 0 deg is less dense than water at 4 deg.

When a lake starts getting cold the water at the top hits 4 degrees becomes dense and sinks to the bottom, this keeps happening until all water in the lake has reached 4 deg. Now when the temp outside drops further the water at the top hits 0 degree abd turns to ice but sice ice at the top is less dense than the water at the bottom it does not sink, so even when you see a lake frozen at the top the water below is still at 4 degrees where aquatic life can survive.
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Read this ..
U can understand easily.

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