Because its ice frozen into a pond and thus, it's called an ice rink
a Zamboni
Theyre are fan forced refrigerator type machines found under neath the rink to prevent it from melting.
A ice rink has a special floor that holds water in it like a pool. It takes about 4-5 hours to freeze the rink. In order to keep the ice rink frozen and solid, the temp. has to be 32 degrees or less....
The cold air/room cools the water and then it adventually freezes (not all the way though or you wouldn't be able to skate!)