What is the Loch Ness Monster? Why, it is a Water Horse, of course. That may not answer some of the more scientific questions, but before the Loch Ness Monster there was the Each Uisge as they called it in the native tongue centuries before.
Dale Drinnon offers an interesting theory that distribution of lake monsters has a good correlation with distribution of elk (or moose as they are also known by). His thoughts can be found here.
No doubt that elk have been mistaken for lake monsters but can one extrapolate the whole way to make them one and the same? The fact that some countries called elk "water horses" is an interesting point but then again hippopotami are literally called "river horses" but look nothing like long necked lake monsters. That did not stop some Scottish academics of old speculating superficially that the Each Uisge may have had its root in an extinct hippo. This theory is nonsense but the Elk theory demands more respect since these creatures are recent or contemporary inhabitants of such lake areas.
However, Dale goes on to liken some land sightings of Nessie to moose taking to the water. The implication is that moose did not really die out in Scotland thousands of years ago. Can one really explain one animal which is not supposed to be there with another animal that is not supposed to be there? I think this improbable and would have expected a moose carcass to have turned up on some Scottish hillside a long time ago. I would also expect the moose to keep swimming to shore and not submerge.
The idea that such a creature would seed the Each Uisge tradition is troublesome at best. The assumption behind most of these theories is the ignorance of the natives and their inability to distinguish a supernatural entity from a moose (or deer, dog, otter, duck) out for a swim. That is why some folklorists prefer to go for the theory that something more realistically monstrous existed in the racial memories of the locals.
Well, that's also plausible so long as they don't keep on seeing it right up to the present day!
Dale has replied to my comment on his page that elk did not exist in Scotland so what is the point in using them to explain Nessie sightings? Check the link above though the discussion pretty much follows my take on the Greta Finlay case which is erroneously ascribed to a deer. My reply:
Granted, but how many elk and how close to Loch Ness? I would speculate these very few Elk were kept on the landowner's estate and not allowed to escape.
Agreed that water horses were never seen as plesiosaurs. The locals matched them to known animals of their time and they were seen right up to 1933.
Your theory is not that much different to ideas that people mistake common deer for Nessie. How significantly different is the Elk, especially when one is far more likely to see a deer swimming across the loch?
One area the descriptions do not match is that the creature submerges and stays submerged. Elk do not submerged (or deer).
The Fordyce creature is unusual but frankly looks nothing like an elk (big head v small head). Other land sightings describe a creature nothing like an elk or deer. Pre-1933 land sightings also do not have the "expect a monster" mentality of witnesses but still they were startled by the unusual and frightening appearance of the creature. Elk or deer would not evoke such a response.