One thing that will scare off a rearing swan is a rearing horse.
My grandfather got two
beautiful white swans evil avian terrorists for the river behind his place, and gave them fairy tale names, Hansel and Gretel. They began a reign of terror--they routed fishermen, attacked boats & canoes, wouldn't let anyone swim or picnic and they chased my poor grandmother back to the house, 100 yards uphill, hissing, biting and pecking and whomping with their wings. They wouldn't let my pony drink out of the river, and lugging buckets past the swan patrol was hazardous duty. A friend had a horse that would rear up on command, like Hi Yo Silver. We took the horse down to the river--the swan reared up, then the horse reared up, and the swan bullies turned tail and retreated. After that we could chase them on horseback, and we got our revenge with swan roundups, but you never wanted to get caught on foot!