Mokoro are traditionally made by digging out the trunk of a large straight tree, such as an ebony tree or Kigelia tree. Modern mekoro, however, are increasingly made of fibre-glass, one of the advantages of which is the preservation of more of the large endangered trees. The boats are very vulnerable to attack by hippopotamus, which can overturn them with ease. A hippopotamus came up under the mokoro of Jim in our group - very scary, but fortunately no serious harm was done.