In Zoo Tycoon, the Hippo lives in the Savannah biome. It requires lots of fresh water and its preferred foliage is the Water Reed. Hippos are not immediately available in free form Zoo Tycoon games; they are unlocked about 9 months into the zoo's first year of business. Hippos are fairly popular among guests.
In Zoo Tycoon 2
The hippopotamus also appears in Zoo Tycoon 2. However, they are more accurately changed to be from the Wetlands biome instead of Savannah, although they will still do well in the latter. They need lots of water, deep and shallow, and it's hard to keep them happy without it. They are comfortable in exhibits with Greater Flamingoes, and are also fine with beavers. It's smaller cousin, the Pygmy Hippopotamus, is also adoptable in Zoo Tycoon 2, as a Tropical Rainforest animal.
The Hippo is featured in the Zoo Tycoon (Xbox) and lives in the Grasslands Biome. It is unlocked when a zoo reaches a fame level of 4. It is not compatible with any animal except other hippos. It can use the hose interaction and likes wading pools and shelters.