Loch Ness Monster
In 2004, a news team from the British Channel 5 created an animatronic model of Nessie, and placed it in the water. That very same day, large numbers of sightings were reported, in the same area where the model was roaming.
There are numerous theories to explain the reported sightings of the monster, but each one has its problems. Undoubtedly the favorite theory of Nessie enthusiasts is the plesiosaur. The idea that it's merely a legend or hoax is far less appealing.
Plesiosaur is actually a broad term for extinct marine reptile with long necks and flippers, but no one knows what type of plesiosaur the Loch Ness monster might be. The elasmosaur, one of the largest of the plesiosaurs, is the considered to be the best candidate of those animals. There are others that also fit the description.
The infamous photographs taken by Robert H. Rines fit the plesiosaur theory, but with their confirmation as hoaxes they cannot be used as evidence. Plesiosaurs are generally believed to have died off approximately 70 million years ago, and while the survival of Coelocanth gives hope to cryptozoologists, the difficulties of a large, air-breathing reptile never being decisively spotted seem to speak against the possibility of a surviving plesiosaur. In addition, especially for as large a creature as a plesiosaur, the relative dearth of fish in Loch Ness would speak against the capability for supporting an isolated population of large animals.
Besides the hoax photograph, the plesiosaur theory has other problems. Loch Ness was created by glaciation, and the plesiosaur fossil evidence suggests that they lived in warm shallow seas. If Nessie was a plesiosaur, it would mean that, if evolution is true, a breeding population of cold-blooded reptiles survived for millions of years past the last evidence of their existence, swam in to the retreating cold glacial waters surrounding Scotland, and became trapped in the loch.
Probably the most scientifically plausible theory is that the Loch Ness monster could be an eel. Eels fit the hump description much better than the plesiosaur, but one of its faults is that the monster often sticks its head up out of the water, a characteristic not usually attributed to the eel. Another is that no eel has been found that reaches the alleged length of the Loch Ness monster. The largest known eel, the conger eel, reaches about 10 feet long and about 250 to 350 pounds.
The zeuglodon, or basilosaurus, is considered to be another likely candidate for the Loch Ness monster by believers. It is a long, slender, fairly serpentine whale, which is believed to have died out long ago, but a few could conceivably have survived to today. The alleged monster of Okanagan, referred to as Ogopogo, also seems to be this sort of creature. The zeuglodon may actually be too large however; they grew to over 70 feet in length, yet tales of the size of the Loch Ness monster do not seem to exceed around 50 feet in length. It also shares one of the problems that the eel has; it doesn't have a long neck to stick out of the water.
The most likely explanation for many of the sightings was described in New Scientist as a rotting tree. As sunken trees rot they release a gas that could rise to the top of the surface, the trunk and branches of such trees resemble what many of the sightings claim to see. 
Due to the shape of the lake, boat wakes in can create large standing waves that appear to rise above the lake. These elongated shapes might explain many of the sightings. 
What may be the first sighting of the Loch Ness monster was in 565 AD by the missionary Saint Columba, who was visiting Scotland to spread the Gospel. He needed to cross the loch, so one of his followers swam out in the water to reach their boat, which had not been tied properly and had floated away from shore. Then a large creature arose from the water and seemed that it was going to devour the man. Saint Columba ordered the rest of his followers to be quiet, and in the name of Jesus rebuked the monster. The creature drew back "as if pulled by ropes" and the man was left unharmed.
The modern history of Nessie began in 1933 when a new road was completed along the northern shore of the Loch, providing easy access to unobstructed views of the water. Soon after this, a couple spotted an "enormous animal" in the Loch. The Inverness Courier wrote up their sighting, describing what they saw as a "monster;" intense media interest followed; and thus was born the modern legend of the Loch Ness Monster.
On November 12, 1933, Hugh Gray was walking back from church when he saw an "object of considerable dimensions—making a big splash with spray on the surface" of the Loch. Luckily he had his camera with him, so he began taking pictures. Only one of the pictures showed anything. Nessie believers hailed it as the first photographic evidence of the monster. Skeptics, however, dismissed it as a blurry mess that doesn't show anything at all
On April 19, 1934, Colonel Robert Wilson, a surgeon, was driving along the north shore of the Loch early in the morning when he noticed something large moving in the water, so he stopped and took a picture of it. At least, that was his story. For the next sixty years this picture was regarded as one of the best pieces of evidence of Nessie's existence and was known as the Surgeon's Photo. It wasn't until 1994 that the full truth came out. What Wilson had taken a picture of was not the Loch Ness Monster. It was a toy dinosaur's head attached to a toy submarine . Moreover, Wilson hadn't even taken the infamous photograph. He had simply been the frontman for an elaborate hoax.
On May 31, 2007, a video was released that is purportedly Nessie.
It is notable that many of the alleged sightings of "Nessie" occur in spring, immediately prior to the commencement of the tourist season.
Other Scottish Monsters
There is another creature reputed to be living in Loch Morar. It may be a close relative of the monster in Loch Ness. Whatever the Loch Ness monster may be, nearly all scientists are unconvinced of its existence.
- Loch Ness Monster: The Ultimate Experiment.
- “The Loch Ness Saga,” by Dr. Maurice Burton, New Scientist, June 24, 1982, p. 872; July 1, 1982, pp. 41-42; July 8, 1982, pp. 112-113.