Really, the first two are the biggies. Collars are important for identification, state leash laws and for training reasons. I mean, it's pretty tough to train and make a correction via e-collar if you take it off in the water. That said, wearing a collar in a debris-filled river probably isn't a very good idea. At least in a pond or small lake you might have time to get to a hung-up dog, but in a spring runoff river the dog and you might only have seconds to get out of danger before one or both of you succumbs to current, cold, debris or all the above.