Quite so - not qualified to comment. However. To land-oriented persons (myself included) the term up-and-down doesn't necessarily mean 3-dimensional movement; it might, but then might not (eg. they ran up and down the street.) When one considers the stretch of water, up and down might just mean continual flight back and forth??? But then it mightn't?
PS. Wasn't the Sapphire incident abt 150 kms north-east of this incident, on a different lake?