Can You Solve this Ice Diamond Riddle? ft. Vsauce’s Michael Stevens

So it took quite a bit of thought, but I figured out that the water level will go *down.*  An easy way to see this is replacing the diamond with a plastic diamond with exactly the same density as the water.  The ice around the plastic diamond will melt and the plastic will be completely submerged.  Clearly the water level will not change because the volume of water displaced is the same as the volume weight of the ice and plastic that was submerged.  Make the diamond more dense, and you displace *more* water despite the volume of the entire thing remaining the same.  This means that after the ice melts, there is less volume despite greater displacement.  This means the water level goes *down.*  This is true *regardless* of the size of the diamond.  The entire thing could have sank from the beginning, but the water level will still drop as the ice melts.