If you look at the third video that Julie Melvin made with her husband, she points out a shallow crossing that is in line with where the bodies were found (or at least where crime tape remained).
Not everywhere that searchers went, was thought to be where the girls were taken. Searchers are looking for all kinds of things, including items deliberately discarded in the water. That area might be too shallow for divers, so it might have required a walk-through.
At the end of the day it doesn't really matter how they traversed the creek, because there really is no other way to have gained access to where the bodies were found, other than to cross that creek. They did it. That's all we can be sure of at this time.
[video=youtube;yQCv3TeNayk]https://www.youtube.com/watch?v=yQCv3TeNayk[/video]