Hippopotamus stalks three men in Zambia

ZAMBIA, Africa -- A group of boaters on an African safari got a big scare when something started chasing them below the water's surface.

The three men were in a boat in a national park in Zambia when they were stalked by a hippo. Waves could be seen just off the side of the boat before the hippo lunges out of the water.

As the driver picks up speed, so does the hippo.

Wildlife experts say many people don't think hippos are able to run or swim as fast as they do because they are so big.

They aren't known to be aggressive unless they have babies or feel threatened.