In the wild they are semi-aquatic, heading for deep water in the papyrus swamps at the slightest hint of a predator, or to move from grassy island to grassy island. My guess is when it's really hot they would enjoy the water.
I was going to say the same thing - I don't ever recall seeing sitatunga swimming. Then again, I can't really recall seeing a sitatunga exhibit where they were given a deep pool to swim in, just a pool deep enough to wade in, or sit in.
