The irizima is described as a swamp-dwelling animal larger than a hippopotamus and black, with a long neck and rhinoceros-like horns. Its breathing produces 3-foot-high waves in the water. Captain William Hichens described it as having legs like a hippopotamus, "an elephant’s trunk, a lizard’s head, and an aardvark’s tail".
Captain Hichens wrote that:
- "not long ago a madcap fellow trekked up from the Cape and plunged into the Congo forests to catch it. He declared that he saw it crashing through the reeds of a swamp, and that it was the brontosaurus—a huge marsh animal, ten times as big as the biggest elephant. In the Cape Town clubs they called him a liar; but a famous American scientific institute guessed better, and sent out an expedition to capture this 'brontosaurus.' It was never caught. Mishaps dogged the expedition and spoiled all chance of capturing the mystery monster."
E. A. Temple-Perkins suggested the irizima may be a myth made up to explain natural waterspouts.