Simplify the following text for a Grade 6 native English-speaking person.
Original: The hippopotamus is semi-aquatic , inhabiting rivers and lakes where territorial bulls preside over a stretch of river and groups of 5 to 30 females and young .
Simplified: The hippopotamus is semi-aquatic . This means that even though it usually lives on the land , it spends a great amount of time in rivers and lakes where males lead groups of 5 to 30 females and young .