Ole Mikkelsen's Cassie sea serpent sighting off Cape Elizabeth

Casco Bay has a long history of sea serpent reports. In 1779 Midshipman Edward Preble, aboard the Protector, chased a "great serpent" and fired a swivel gun at it, though that encounter is usually placed in Penobscot Bay. In July 1818 the Portland Argus described an animal 80 to 100 feet long in Portland Harbor. The creature came to be known as Cassie, a name credited to cryptozoologist Loren Coleman.

June 5, 1958. Ole Mikkelsen, a Portland commercial fisherman, had gone out before daybreak with his partner, Ejmar Hairgaard. By about 6 a.m., half an hour after sunrise, they were working nets roughly five miles off Cape Elizabeth. The anchored Portland Lightship lay about a mile and a quarter to the north. The morning was hazy.

Something came toward them out of the haze. At first they took it for a submarine. Then they realised it was alive.

Mikkelsen was certain it was "well over 100 feet long." Its head was broader than its neck and held out of the water. It was the colour of a cusk, with a lighter underside to the neck. It had "the tail of a mackerel," which rose from the water each time it dived. He could make out no eyes or ears, but he was sure it could hear.

Every three or four minutes it went under and came back up. Once it surfaced about 125 feet from the boat and stopped, as if to look them over. Hairgaard called for a knife. If it came any closer, they would cut the nets and run for the lightship. It turned away instead.

Then came the detail that stayed with the story. Every time the foghorn on the lightship sounded, the animal turned its head toward it. After more than 45 minutes it turned and swam southeast into the haze.

No newspaper reported the sighting in 1958. The account surfaced in 1985, or 1986 by one telling, after Coleman spoke about cryptozoology. As he told NewsCenter Maine: "I was giving a talk at the Appalachian Mountain Club, and a man came up and said you should really talk to an old friend of mine." Mikkelsen was then 81, and Hairgaard had died. Coleman later said of the interview: "He was living it all over in front of me."

There are no photographs, no film and no lightship log entry. The account rests on one surviving witness, recalled about 27 years after the event. Tellings differ on details such as the colour, which some versions give as "colored like a flounder." Writing in general terms, Emily Burnham of the Bangor Daily News noted that when sailors report sea monsters, "the vast majority of the time, they've actually spotted sharks, whales or squid." No one has accused Mikkelsen or Coleman of a hoax.

Coleman himself has suggested that sea serpents are "more likely … mammals rather than snake-like animals." In 2016 he added that "the sea serpents that are out there now know how to avoid those ships."

The 1958 encounter is usually called the last known sighting of Cassie. It appeared in print in Portland Monthly in May 1986. Coleman retold it in Mysterious America and in The Field Guide to Lake Monsters, Sea Serpents, and Other Mystery Denizens of the Deep, written with Patrick Huyghe. NewsCenter Maine revisited it in 2016. The International Cryptozoology Museum in Portland now displays Cassie material.