There is a history of sea serpent sightings. Here are some of the most well known.
On August 6th, 1848, the Royal Navy frigate HMS Daedalus was cruising near the Cape of Good Hope when the Officer of Watch spotted an object in the sea. He drew the attention of the Captain and several crew members on deck to it. It was a large sea snake, or sea serpent, that they estimated to be sixty feet long, 15 inches in diameter, and moved through the sea with it's head some four feet out of the water.
1937 Alfred Peterson, a nurse aboard a British troopship in the China Sea, spotted what at first he thought was a big tree floating in the sea. A few minutes later it was still there, keeping pace with the ship. It was a 25 foot long, grey-black, body with a head shaped like a giraffe.
The most accepted sighting to date was by three fellows of the Zoological Society of London. Their account of "a creature of most extraordinary form and proportions" is recorded in the 1906 edition of the Society's Proceedings and in Nicoll's 1908 book Three Voyages of A Naturalist.On December 7, 1905, at 10:15 AM, Nicoll and Meade-Waldo were on a research cruise aboard the yacht Valhalla. Fifteen miles east of the mouth of Brazil's Parahiba River, Nicoll spotted a large dorsal fin which "resembled that of no fish I had previously seen."Nicoll turned to his companion and asked, "Is that the fin of a great fish?" Meade-Waldo looked. The fin was cruising past them about a hundred yards from the yacht. Meade-Waldo described it as "dark seaweed-brown, somewhat crinkled at the edge." The visible part of the fin was roughly rectangular, about six feet long and eighteen inches to two feet high.Meade-Waldo turned his binoculars on the object, and immediately a head on a long neck rose from the water in front of the frill. He estimated the neck was "about the thickness of a slight man's body, and from 7 to 8 feet was out of the water; head and neck were all about the same thickness."The head had a very turtle-like appearance, as also the eye," Meade-Waldo wrote of the incident. It moved its head and neck from side to side in a peculiar manner: the color of the head and neck was dark brown above, and whitish below-almost white, I think."The neck threw up a significant wave where it entered the water, and Nicoll noted that, "Below the water we could indistinctly see a very large brownish-black patch, but could not make out the shape of the creature."Nicoll added, "This creature was an example, I consider, of what has been so often reported, for want of a better name, as the 'great sea-serpent.'"In a 1929 letter to sea-serpent writer Rupert T. Gould, Meade-Waldo added that "I will never forget poor Nicoll's face of amazement when we looked at each other after we had passed out of sight of it."The sighting lasted for several minutes. At 2:00 AM on December 8th, however, three crewmembers saw what appeared to be the same animal, almost entirely submerged, overtaking and passing the Valhalla at a speed of about nine knots.
Most people would accept this account as genuine as the fellows concerned were naturalists and scientists, one would hope not easily fooled by seeing a mating whale or other such explanations given for sea serpent sightings.
I wonder if there have been any more modern sightings That have not been recorded?