Yup! 'Seen that from the inside when my student made a landing error - not good. Though the landing place was chosen better than it could have been, with river banks for reference, it was still more in the middle than I would have chosen for a glassy water landing. Glassy water, as any uniform surface, is nearly impossible to judge height from. The aircraft must be landed by carrying a correct flare all the way down from a suitably high height, to contact with the surface in that attitude. Doing so requires carrying power down the flare, and removing power after contact with the surface. Glassy water landings are the most common need for this technique, though skis on unbroken snow can need it too.