"The Devil's Kettle" is an unusual waterfall located on the
Brule River, Minnesota, 1.5 miles (2.4 km) from its mouth. The river splits in two to flow around a mass of
rhyolite rock. The western flow surges into a pothole, falling at least 10 feet (3.0 m), and disappears underground. It is believed the water rejoins the main channel of the river or has a separate outlet into Lake Superior, but it has never been located. Researchers have dropped brightly colored dyes, ping pong balls, and other objects into the Devil's Kettle without result.