The object is a tree branch or other debris. The physical dynamics of Loch Ness create water currents, which are counter intuitive. It is also the case, that upto 30% of observers will perceive a "head" on any vertical object such as a tree or branch.
(See Shine and Martin 1988, p:170 and Shine 1993)
A log in Loch Ness
Courtesy Richard Carter
