THE CATCHER IN THE RYE (J.D. SALINGER) AND THE ANOMALOUS PROPERTIES OF WATER

There is a recurring joke in the book: Holden Caulfield asks various  characters what happens with the ducks of Central Park´s lake or where they go when it becomes frozen at winter. Most  people get angry at  the question, but there is a taxi driver  that, apart from getting angry,  responds with some basis: he says  nothing about the ducks, but  states that the fishes stay at the lake  during winter time.

  And he is right, because under the ice surface there is water where  fishes can live. I guess water is the only substance that in solid form shows a lower density than as a fluid  and so it´d float over. Because of this property, life is possible in the poles.  

But, what happens with ducks? They also stay at the lake in Winter (and it seems they  could  leave more easily than  fishes if they wanted to), they stay right  at the center of the lake, because this zone never gets frozen.