Ok, so maybe it was never really lost, but since it's closure in 2001, River Country the first water park at Walt Disney World, has pretty much been forgotten about. Recently though, someone happened upon the ruins of River Country and snapped some shots. From what it looks like, Disney is content to let it rot. The structures and the slides are still there, but the swamp has overgrown everything.
To view the pictures of the ruins, please do a google search on River Country - The DIS Discussion Forums - DISboards.com