In article , Dave Smith writes:
There is a similar question about a boat full of iron ore sinking in a canal
lock. The water level does not change because floating objects displace water
equivalent to their weight.

And sunk objects displace water equivalent to their volume.

A boat full of iron ore has a density greater than that of water, else
it would not sink. Accordingly, the volume it displaces when sunk
is less than the volume it displaces when floating.

The level in the canal goes down.