However, the key point, is on glassy water or unbroken snow, you really do not know where the whole plane is!
I'll second Pilot DAR's comment. I remember a glassy-water landing on a lake in BC where I was absolutely convinced that the floats were about to touch the water and yet it was at least another 10 seconds (and 50' or so of altitude) before there was that lovely hissing noise as the keels touched. Unless you've experienced it yourself, it's hard to believe how strong the illusion of being close to the water is.
I've read in float-flying books that one option is to throw out a cushion or life-jacket to give an aiming point and height reference for an approach. Just hope there are no TC/FAA/CAA inspectors watching and waiting to write you up for dropping things from an aircraft
