That would be about right - water is densest at 4°C so sinks to the bottom at that temperature - colder water is less dense and floats on top, it is this property which ensures open bodies of water freeze top down so fish and other aquatic beasties have a chance of surviving the winter.
Isn’t whoever designed that wonderful, even considering the poor little fishes? Of which there are none in my pond, because I never put any there and the only way they could arrive is if a bird accidentally dropped a couple. 
About 10 or more years ago a stork arrived but after scanning the situation he left, never to return, I didn’t tell him about the frogs, even though I would love his company. 
1 Like
Also why icebergs float. It’s reckoned that without waters somewhat peculiar properties, life on Earth would probably never have started, or if it did, may not have gone beyond the prokaryote stage.
… or even remained amateurkaryote!
3 Likes
Plus the fact that icebergs are frozen fresh water and sea is salt water and therefore denser.
1 Like
The vast majority are, but not all are in salt water though. You do get some in fresh water when they calve from glaciers into fresh water lakes.