Water at about 4°c (39°f) is more dense than water at 0°c (32°f). why would the living organisms in the lake die if the water at the freezing point was denser than the water at 4°c?

the water would freeze across the surface of the lake, blocking sunlight necessary for photosynthesis.
the water would freeze across the surface of the lake, blocking the dissolving of oxygen and nutrients.
the freezing water would sink before it could freeze, preventing the lake water from freezing.
the freezing water would sink to the bottom and freeze the lake water from the bottom up.