Several generations of my family are buried in Longstraw Cemetery, so I was curious when I saw this question. I asked my parents and they've never heard of a relocation. My mother contacted her cousin who is in his 90s, and he hadn't heard of it. She is trying to get in touch with a friend of hers who used to oversee the cemetery - will let you know if she has any information about this.
My great-grandmother is one of the people buried there and she died in 1918 and was not moved, so if there was a relocation, it may have been before then.
They said that some migratory railroad workers died of some kind of epidemic and were buried in an unmarked grave(s)on the east side of the cemetery, but these graves are now outside of the cemetery as the fence was moved at some point, I gather due to road widening. Maybe this has something to do with relocating some graves, although there is no body of water involved.