That's in Homosassa Springs, Florida! I went there as a kid. It is so awesome. They have a bunch of manatees too. The sign means what it says by the way.
Hippos attract mates by marking territory, urinating and defecating at the same time. Then, an enamored hippo will twirl its tail like a propellor to spread this delicious slop in every direction. This attracts lovers, and a pair will begin foreplay, which consists of playing by splashing around in the water before settling down to business.