You don't have to buy a fishing license within the boundaries of Mammoth Cave National Park, but state size/creel limits apply.

I would say that a National Forest is not the same deal...you likely have to buy an Indiana license. The Daniel Boone National Forest makes up a part of Eastern Kentucky, and you have to buy a fishing license for any kind of fishing within its boundaries, so I'd say Hoosier National Forest is the same way.