My brother and I also aggravated a swan while we were out for a walk on the Boise Greenbelt.
She swam up and started hissing, but never climbed out. Paul was hoping that she'd get out and start chasing us. He was telling me about some of the other more aggressive ones that would chase runners down the trail. Also, that if there were couples and the swan started chasing the girl, that the boys would generally ditch the other half and run for their lives.