It is a very small island in the middle of a small man-made lake (called Rivers of America.) You can take small rafts out to the island and let the kids run around a bit. (Or at least you could before the new pirate-theming was being added.)
There are also two ships that travel the loop around the Rivers of America, one a sailing ship and the other a riverboat. You can ride on the ship(s) for a brief scenic tour.