It's called Disney's River Country. The park opened in 1976, the theme behind it was that it was supposed to be an 'old-fashioned swimming hole.' The park had rustic and wilderness elements, including man-made rock formations that are similar to those in Big Thunder Mountain Railroad in the Magic Kingdom.
The park was closed in 2001, and Disney later announced in 2005 that the park was to be closed for good. Although there are a number of theories as to why Disney closed down the park, they haven't commented on the reason. One of the most popular theories is that the park got its water from a nearby lagoon.
The lagoon, stories say, was contaminating the water in the park and would have cost too much to redo. The most likely reason is that by that time, there were already 2 other, much bigger parks that made River Country unprofitable.
The park has not been demolished, and if you're sneaky, you can go in and take a look at the park. The rustic feel gives it a very eerie ghost-town feel. Check out the video below to see a couple of guys going through the park!