Water fall was built sometime between 1971-1976. It's only a guess that as time has passed, the concrete "rocks" have possibly aged and weakened to the point it is not advisible by their insurance carrier to allow guests to walk under it anymore. I don't know what year they began blocking the path. The "cave" at the old float trip ride, now American Plunge, was replaced a few years ago with a new concrete tunnel as it apparently aged to the point it needed replacement. Also remember the waterfall feature in front of Grandfather's Mansion? It too disappeared as the concrete aged. It has been cheaper, apparently, to remove the old water structures rather than rebuild them. The park consistantly has tried to find ways to lessen their expenses while increasing profitability. That's business, but some of the old character of the park has vanished, probably forever.