We made several visit to Hippo pools. The first one at Lake Manyara was somewhat sedate. When we first got there all we saw in addition to a few birds were a few blobs that looked like small islands. Then a couple of minutes later one of the Hippos emerged. A few days and several hippo pools later we got to this one which was chock full of hippos wallowing in a very muddy, smelly pool - a bit like a massive cesspool. This is a ~30 second movie.