Japan is certainly a land with its fair share of mysteries, spooky folklore, legends, and strange beasts. One place where bizarre monsters are said to roam here is in the many rivers that cut through this enchanting land, and which have long perplexed the residents of these areas. From giant fish and snakes, to man-eating seal monsters, to dog-sized hissing water rats, it seems the waterways of Japan are a veritable menagerie of the weird. Here we will look at some of curious aquatic cryptids that seem to call Japan's rivers home.

One very early case of something strange prowling Japan's rivers comes from the 1800s, when an unidentified river in Japan was said to be inhabited by a population of strange, fierce seal-like creatures said to attack and disembowel anyone who came across them, yet leave the bodies uneaten, possibly due to being attacks out of territoriality rather than for food. The animals were described as being 4 to 5 feet long, with scaly, fish-like bodies, seal-like faces, sharp teeth, and human-looking manes of hair on their heads and necks. They were said to often haul themselves out of the water to congregate on the banks of the river where they would engage in rowdy, boisterous behavior, playing and fighting amongst themselves while filling the air with their relentless barking cries. These creatures were mentioned in the 1823 book The World in Miniature, by Frederic Shoberl, as well as in a 1996 article in Strange Magazine by Karl Shuker called "Hairy Reptiles and Furry Fish." Since the river remains unidentified and there are no modern accounts of these creatures, it is difficult to figure out what they could have been, if anything.

Another very early case of something strange and enormous prowling Japan’s rivers was frequently reported during the Meiji Era (1868 to 1912). Most commonly known as the Ryuu Gyo (Dragon Fish), this monstrous fish was said to be up to 8 to 10 feet in length and sporting a reptilian, alligator-like head and covered in bony armored plating. One of the earliest reports came from the area of what is now Ibaraki prefecture, where villagers claimed to have captured one of the creatures in their nets in 1873. The gigantic fish was said to be 8-feet long, with a formidable, gaping maw filled with wicked fangs, and the whole of the body dotted with hard bony protrusions of some sort. The fish was exhibited until it began to rot, after which it was thrown back into the river and lost to history.

Another account from 1875 concerns a fisherman whose nets were ripped to shreds by one of the beasts in a river in what was called Watarai province, this time a specimen said to measure a whopping 10 feet in length. The fisherman was able to track it down and finally capture it, and it was found to be a fish very similar in appearance to an alligator but with fins instead of legs and scaly, bony armor covering it. In this case some brave villagers reportedly tried eating its flesh, but it was described as foul-tasting and pungent. Again the carcass was discarded.

In 1888 there was a rather dramatic account of a local who claimed to have seen one of the Dragon Fish, said to be around 10 feet long, dark in color and with long “spines” along its back lurch out of the water to try and grab a deer that had been drinking by the riverside. The startled man called out to his fellow villagers, but the massive mystery fish was gone by the time anyone arrived. One common theory as to what the Dragon Fish could have been is a large sturgeon, but these are not native to the areas where they were reported, and considering there are no modern sightings of the Dragon Fish we may never know for sure.

Perhaps one of the most unusual of the giant mystery fishes of Japan’s rivers is a remarkably odd, winged creature that has been sighted in the Nagara River, of Gifu prefecture. The first reported sighting of the creature was brought forward in 1986, when a large fish measuring approximately 7 feet long and possessing distinctive ray-like “wings” was seen flying through the water by a local resident. The eyewitness said that he had never seen anything like it in the river before, and described it as looking just like some sort of massive ray. In the summer of 1998 there was another remarkable sighting when a group of people taking in the scenery from a bridge over the river was surprised to see an enormous round fish like a ray glide through the water on wings beneath them before passing out of sight. The strange creature was purportedly witnessed by at least 10 people at the time.

Another strange sighting of the beast was made by a group of elementary school children as it swam in a deep pool in the late 90s, and their attending teacher saw it as well, describing it as measuring 6.6 feet from wingtip to wingtip. The group allegedly watched it languidly glide about near the surface for a full 10 minutes before it sank from view. There have been other sporadic sightings of these bizarre river-going rays over the years since, yet sadly no photographic evidence has come forward that I am aware of at this time. A freshwater giant ray would not be so unusual in and of itself, as some of the largest rays in the world are freshwater varieties, such as the Mekong River giant freshwater stingray of Southeast Asia, which has been known to get up to 5 meters (16.4 feet) long and 600 kg (1,300 lbs) in weight, making it truly a river monster. The thing is, Japan has no known species of freshwater ray like this, so whatever people are seeing in the Nagara River has been left up to debate.

Mekong River giant stingray

One curious mystery beast that was reported from rivers throughout the country in the 1960s and 70s was what appears to be have been some kind of large, aquatic rat-like creatures purportedly the size of a dog. The strange creatures were usually reported at dusk or night, and often described as having reflective eyes. These giant rats were said to always be seen in or near the water, and that they would hiss or make a rattling noise, and otherwise act aggressively if approached. It is mostly thought that what people were seeing were most likely nutria, also called coypu (Myocastor coypus), which are very large semi-aquatic rodents originally native to South America that typically live along rivers and in marshlands. Although not native to Japan, nutria were introduced here in 1910 as a source of fur. When fur prices dropped, many of the nutria fur farms which had sprouted up around the country to meet demand went under and subsequently released the nutria into the wild. Since that time, the population of wild nutria in Japan has skyrocketed, and they have taken to their new home just fine.

The Tone River, of the Kantō region of Japan’s Honshu Island, has long produced reports of some sort of mystery creature, in this case an enormous fish of some kind with a dark grey back that has led to its nickname, the “Grayback.” These creatures are reported as being from 6 to 8 feet in length and are most commonly said to be slow moving, often seen leisurely bobbing up to the surface only to dive back down again. One account comes from a group of people who observed a giant fish around 9 feet in length casually swimming along for several minutes from one of the many bridges that span the river. The gigantic fish eventually slowly sank down out of sight as the surprised onlookers watched in amazement. It did not resurface.

A more harrowing report was given by a fisherman that a huge fish with an oversized head appeared out of the depths and circled slowly around his boat for some time. The man reported the powerful fish as being approximately 3 meters (10 ft) long, a size he was able to confidently estimate since the fish was as large as his own boat. The eyewitness said that on several occasions the colossal fish came so close to the boat that he began to fear that it might actually be capsized by the beast. Yet another fisherman told of having his boat actually nudged by one of the giant mystery fishes. Although there are plenty of rather large carp in the river, there is nothing that comes remotely close to the sizes reported for the Grayback. Other ideas include that it is a wayward shark that travelled inland, a pinniped, or even a lost baby whale that somehow got stuck in the river. Nobody knows, but the reports keep coming in from time to time.

A stretch of the Tone River

Interestingly, an offshoot of the Tone River, the Edo River, also has several mysterious creatures which have been reported in its waters over the years. One of the more widely known is some sort of massive fish frequently sighted that is said to be around 2 meters (6.6 feet) in length and with a stocky, fat body that is silver in color. The shy creature is often seen casually hovering close to the surface, only to make a big splash if approached, much to the surprise of fishermen and hikers along the riverside. At least one fisherman has even told the tale of catching the beast, only to have the behemoth break his line and get away. The giant fish, which is most frequently theorized to be some species of outsized carp, is so well-known along the river that it has even gained the affectionate nickname “Eddie,” which is an homage to the name of the river and the more famous Nessie lake monster.

Also widely sighted in the Edo River during the 1970s was a bizarre, seal-like creature most commonly reported as being around 7 feet in length, with a face like a cat, long arms ending in sharp claws, a somewhat elongated neck, sagging skin, a long thin tail, and a distinctive cat-like mewl. The strange beast was seen exclusively in the year of 1973, when there was an intense wave of sightings in the portion of the river passing the city of Matsudo, in Chiba prefecture, and since it was a relatively urban area and apparently the thing was not shy at all it was seen hundreds of times.

The creature would be called the Matsudodon, and was not only apparently not afraid of being seen, but at times was downright bold, even playful. One fisherman out in a rowboat reported having the creature pop up from right below his boat, after which it circled him and rolled about in the water, almost as if it wanted to play, before suddenly diving down with a dramatic splash of its tail. The fisherman would report that he had had the distinct feeling that the beast was merely curious and non-threatening. On another occasion, a jogger claimed that he had seen the creature out in the river doing jumps and spinning in the water as if amusing itself, and another eyewitness allegedly saw it tossing about a piece of floating garbage as if it were a ball.

One account was relayed personally to me by an elderly local, who claims that at the time she would actually go out to the river and toss it fish, which it would snap up with relish. According to this witness, the Matsudodon would come by every day at around the same time to receive these handouts, and would get rather close to shore. She said that at no point did it seem aggressive or scared, and she also stressed that it was not a seal of any kind and that it could grasp and manipulate things with its “hands.”

The Matsudodon was sometimes seen by large groups of people, such as a crowd of curiosity seekers who gawked at it from a bridge as it leisurely cavorted in the water below and let out cat-like mewling noises. On another occasion a group of friends reported seeing the creature sunning itself out of the water on the riverside. The creature was only ever seen in the area of Matsudo and only for a brief span of time, leaving the impression that whatever it was it was probably only a passing visitor. Since the Edo River connects to Tokyo Bay it has been speculated that it could have been something that wandered in from the sea by accident and got lost, although what that could be is anyone’s guess. Was it just a misidentified seal or something more mysterious? We will probably never know.

Also from the Edo River are reports of extremely large eels of some kind. In one report, a group of workers were doing construction on a floodgate when they noticed four giant eels measuring between 6 and 8 feet long and seemingly slow and lethargic. The workers then allegedly went off to get something to catch them with, but when they returned the strange creatures were gone. A fisherman also claimed that he had seen a massive eel around 7 feet in length swimming about near a bridge.

Perhaps even spookier than giant eels are reports of what seem to have been giant snakes in the Edo River. In 1978, a group of teenagers reported seeing what they thought was a floating log at first until it began to undulate and proved to be a snake-like creature swimming through the river in the area of Nagareyama, in Chiba prefecture. The enormous snake was reported as being around 25 feet in length, and they watched it until it swam into a tangle of reeds and disappeared.

That very same year a man was out at dusk looking for crayfish when he heard a splash not far away. He claims that he looked out to see an elongated dark shape in the water, and that when he shone his flashlight towards it he could see that it was a snake with its head over the surface, and that it had huge saucer shaped eyes that luminously reflected the light like those of a cat. The serpent was alleged as being over 20 feet in length. The only thing that comes to mind with such reports is that it could have been a large water-loving snake such as an anaconda, but these don’t exist in Japan and probably would not appreciate the cold weather here. Were these some sort of sea serpent wandered in from the sea? Who knows?

It is interesting that in a land that many people consider to be overcrowded and fully explored that there could be so many anomalies prowling about on the fringes. Yet this is still a land with its remote, wild places and places and its mysteries that remain in the shadows. What are we to make of the cases that we have seen here? Are these cases of misidentification or exotic escaped animals, or are they something from beyond our current knowledge? No matter the answers to these question, it seems that if you are ever in Japan it may be worth taking a stroll along one of its many rivers. You just might see something remarkable indeed.

Brent Swancer

Brent Swancer is an author and crypto expert living in Japan. Biology, nature, and cryptozoology still remain Brent Swancer’s first intellectual loves. He's written articles for MU and Daily Grail and has been a guest on Coast to Coast AM and Binnal of America.

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