A ""why"" story, telling how Hippo got permission to go into the water even though the god Ngai had told him that he was a grass-eating land animal, by promising to open his mouth wide to prove he isn't eating fishes and to stir up the bottom with his tail to show he isn't hiding bones. Though simply plotted, the pungent dialogue leads to a satisfying resolution as Hippo negotiates with the god. A neatly humorous twist when he jumps into the river, sinks ""like a stone, because he couldn't swim"" but learns to hold his breath and run along the bottom, makes a pleasing conclusion. The watercolor illustrations are glorious: the African setting burning red under a torrid sun, the god mysteriously part of a dusky mountain, the underwater scenes muted and cool, and plenty of indigenous flora and fauna. This is perfect for picture-book hour as well as for individual delectation.