There is plenty of activity at Jellystone.
For those who want to swim - three pools and lake.
Basketball courts and tennis too.
For the more adventuresome, you can rent a canoe or paddle boat and you can even fish in the lake. Although it is mostly bluegill and carp and least from the catches I've seen.
For the kids there is a Yogi Bear mini-golf course and it is a great beginner course. My three-year-old nephew loved it.