Attack of the Mute Swans: 30-pound birds dunk Indiana swimmers

The Indiana Department of Natural resources is warning swimmers never to tease or harass a mute swan. It's not nice. Moreover, judging by this Associated Press story, if you do, these 30-pound birds may come up behind you and—without warning of course—pull you underwater.
http://www.indystar.com/apps/pbcs.dll/article?AID=/20060607/LOCAL/606070517