Issie, or Isshī, is a lake monster said to inhabit the 41 square kilometre, 764 foot deep Lake Ikeda. Lake Ikeda is the largest lake in Kyushu and is located in the Kagoshima Prefecture. Issies are said to be about 40 to 50 feet in length, with shiny black skin, and serpentine bodies. They are often reported to have one or more humps on their back.
Although comprehensive reports of a creature inhabiting Lake Ikeda are more recent, the folklore of issie is much older. Historically, the lake was heavily associated with ryujin, an aquatic dragon in Japanese mythology.
The first detailed sighting was on September 3rd, 1978, when more than 20 people, mostly in the Kawaji family, observed a creature on Lake Ikeda's otherwise calm surface. The first to notice was the son of Yutaka Kawaji, who pointed out a 16 foot-long hump that was raised about two feet out of the water. Yutaka then ordered the children to go back inside, and he got on his motorboat to get closer to the animal, which was now swimming away. Yutaka was unable to get close, but he managed to observe the creature for three to four minutes before he lost track of it.
Yutaka was understandably very intrigued by his encounter, so he purchased a 135 mm lens camera in hopes of seeing it for a second time. Unfortunately, he never saw the creature again.
Three months later, on December 16th, 1978, a man named Toshiaki Matsuhara visited the lake, as he was interested in the folklore of the area. Surprisingly, Matsuhara managed to see and photograph what appears to be a large, serpentine animal slithering in the water (above). The object in the photo, if real, would likely be some kind of eel, based on its very long, scaly body and left-to-right swimming motion, which is not known in any mammal species.
The tourism department of the nearby city of Ibusuki made a 100,000¥ reward (or 1,542 USD in today's money), for any photographic proof of issie. When Matsuhara heard about the reward, he submitted his photo and received the money/
In January of 1991, a group of "Issie researchers" filmed a 50 foot long, black creature swimming in the lake. The footage was later shown on the show Sekai No Shinpi-Tekina Gensho, or “worlds mysterious phenomena.”
Lake Ikeda is a caldera lake, meaning it formed when the ground surface above a volcano's magma chamber collapsed downward into the empty chamber, leaving a massive cauldron-lake depression, which then filled with water. Lake Ikeda formed only 6,000 years ago and is not connected to any nearby bodies of water, meaning that if issie exists, how it managed to get there is unknown.
A common theory explaining the origin of issie is that they are misidentified giant mottled eels (Anguilla marmorata). That said, they rarely exceed six feet, nowhere near issie's reported length of 40 to 50 feet.