Video shot by David Roseman, who works in Wood Tikchick State Park in southwestern Alaska part-time, shows a clear view of the bear using its strong legs to propel itself into the water. With small bear cubs, only a few months old, sitting perched atop its back, the mother ferries them to the shore.

"I was heading to do a fuel run for the lodge and just saw something in the distance. I was probably within 30 yards," said Roseman.

Roseman has worked in the park for 21 years, but in the time he's been there, he's never seen cubs float across a lake on their mother's back.

Despite their large hefty bodies and thick fur, brown bears are great swimmers.

Wayne Kasworm, a