The mechanism by which lakes freeze from the top down

Question

It is my understanding that within a given medium warmer substances tend to rise and cooler substances fall, i.e. warmer air above cooler.

Assuming the same is true with water then in a lake the cooler water should fall to the bottom while warmer water rises to the top, correct? If so, I would expect that lakes would freeze from the bottom up. Can you please explain why this isn’t the case?

Thanks for your explanation.

In: 23

Answer 1

Water is at its densest at 4°c and gets less dense as you approach 0°c leading to the odd effect of bodies of water freezing from the top down as opposed to bottom up as that denser 4°c water settles at the bottom and the cooler 0°c water ends up at the top.