Mokèlé-mbèmbé (meaning "one who stops the flow of rivers" in the Lingala language) is a legendary water-dwelling creature of Congo River basin folklore, sometimes described as a living creature, sometimes as a spirit, and loosely analogous to the Loch Ness Monster in Western culture. It is claimed to be a sauropod by some cryptozoologists.
Expeditions mounted in the hope of finding evidence of the Mokèlé-mbèmbé have failed, and the subject has been covered in a number of books and by a number of television documentaries. According to skeptic Robert T. Carroll, "Reports of the Mokèlé-mbèmbé have been circulating for the past two hundred years, yet no one has photographed the creature or produced any physical evidence of its existence." The Mokèlé-mbèmbé and its associated folklore also appear in several works of fiction and popular culture.
According to the traditions of the Congo River basin the Mokèlé-mbèmbé is a large territorial herbivore. It is said to dwell in Lake Tele and the surrounding area, with a preference for deep water, and with local folklore holding that its haunts of choice are river bends.
Descriptions of the Mokèlé-mbèmbé vary. Some legends describe it as having an elephant-like body with a long neck and tail and a small head, a description which has been suggested to be similar in appearance to that of the extinct Sauropoda, while others describe it as more closely resembling elephants, rhinoceros, and other known animals. It is usually described as being gray-brown in color. Some traditions, such as those of Boha Village, describe it as a spirit rather than a flesh and blood creature.
The BBC/Discovery Channel documentary Congo (2001) interviewed a number of tribe members who identified a photograph of a rhinoceros as being a Mokèlé-mbèmbé. Neither species of African rhinoceros is common in the Congo Basin, and the Mokèlé-mbèmbé may be a mixture of mythology and folk memory from a time when rhinoceros were found in the area.
Numerous expeditions have been undertaken to Africa in search of Mokèlé-mbèmbé. During these, there were some sightings that have been argued by cryptozoologists to involve some unidentified dinosaur-like creature. Additionally, there have been several specific Mokèlé-mbèmbé-hunting expeditions. Although several of the expeditions have reported close encounters, none have been able to provide incontrovertible proof that the creature exists. The sole evidence that has been found is the presence of widespread folklore and anecdotal accounts covering a considerable period of time.
According to science writer and cryptozoologist Willy Ley, while there are sufficient anecdotal accounts to suggest "that there is a large and dangerous animal hiding in the shallow waters and rivers of Central Africa", the body of evidence remains insufficient for any realistic conclusions to be drawn on what the Mokèlé-mbèmbé may be.
According to the writings of biologist and cryptozoologist Roy Mackal, who mounted two unsuccessful expeditions to find it, it is unlikely that the Mokèlé-mbèmbé is a mammal or an amphibian, leaving a reptile as the only plausible candidate. Of all the living reptiles, Mackal argues that the iguana and the monitor lizards bear the closest resemblance to the Mokèlé-mbèmbé, though, at 15 to 30 feet (9.1 m) long, the Mokèlé-mbèmbé would exceed the size of any known living examples of such reptiles. Mackal believes the description of the Mokèlé-mbèmbé is "consistent with a small sauropod dinosaur".
Mackal also judged the existence of an undiscovered relict sauropod to be plausible on the grounds that there were large amounts of uninhabited and unexplored territory in the region where a creature might live, and on the grounds that other large creatures such as elephants exist in the region, living in large open clearings (called "bai") as well as in thicker wooded areas.
However, other researchers have argued against the existence of Mokele Mbembe. According to Daniel Loxton and Donald Prothero, the conventional image of Mokele Mbembe held by cryptozoologists such as Roy Mackal is based on an outdated image of sauropod dinosaurs from the early twentieth century. For example, most sauropods did not live in swampy areas and subsist on aquatic plants. Instead, they lived in seasonally dry woodlands and ate tough conifers and cycads. This suggests that Mokele Mbembe sightings are not of a real sauropod dinosaur population but are instead the attempts of cryptozoologists to fit ambiguous eyewitness accounts into an outdated image of sauropod dinosaurs. Loxton and Prothero also argue that a surviving population of sauropod dinosaurs would leave behind skeletal remains like other large animals do and the rich fossil record of Africa should contain dinosaur bones younger that 65 million years old if a group of non-avian dinosaurs had survived to the present. The absence of this evidence despite several centuries of Western contact with the region and numerous expeditions in search of the animal argues against the existence of Mokele Mbembe. The failure of aerial surveillance and satellite imagery to detect these large animals while being able to detect other large animals like elephants also argues against the existence of Mokele Mbembe.