Lynda Tyler, who lives on the shore of Big Lake in Wasilla, filmed the girls on a personal watercraft, the Anchorage Daily News reported. Houston Snyder, owner of the Big Lake Lodge, posted the video on YouTube, giving the incident national publicity.
No one is completely sure if the cygnet -- a baby swan -- was killed by the girls. The swan family had four cygnets when they were videotaped and three when they showed up Wednesday at the lodge dock.
Bruce Woods, a spokesman for the U.S. Fish and Wildlife Service, said an agent would go to the lake to investigate the incident. But he said nothing can be done unless the girls are identified -- and even then they are most likely to get a lecture on the U.S. Migratory Bird Act and being careful around wildlife.
The lake has long been a getaway spot for people from Anchorage, known for its waterfront bars. But residents say it has become quieter and birds have been returning.
2014: The Year in Music [PHOTOS]