The Devil's Kettle

Summary

The Brule River splits at a rock outcrop above Lake Superior. Half of it goes over a waterfall. The other half falls into a pothole and disappears, and for decades nobody could say where it went.

People threw things in to find out: ping-pong balls, dye, logs, and, in the durable local legend, a car. Nothing was ever seen to come out. Theories included an underground river, a lava tube, and a fault line running to the lake.

In 2017 a state hydrologist finally did the obvious thing. He measured how much water was going in above the falls and how much was coming out below.

They matched.

What is documented

The site. In Judge C. R. Magney State Park on Minnesota's north shore, the Brule River divides around a rock formation. The eastern channel drops down a conventional waterfall. The western channel drops into a large pothole, the Devil's Kettle, and vanishes.

The objects. Over the years, people threw things in to trace the water. Ping-pong balls. Dye. Logs. Coloured markers. None was ever observed to emerge anywhere. The story that a car was pushed in is folklore and is not documented, but it is a very good indication of how seriously the problem was taken.

The theories. An underground river carrying the water to Lake Superior. A lava tube in the region's volcanic basalt. A fault line. All of them require the water to travel some distance through the rock and emerge somewhere that nobody has found.

The measurement. In February 2017, Jeff Green, a hydrologist with the Minnesota Department of Natural Resources, and colleagues measured the volume of water flowing in the river above the falls, and the volume flowing in the river below.

The figures came out at roughly 123 cubic feet per second above, and roughly 121 below. The difference is within the error of the measurement.

There is no missing water. It never left the river.

Leading explanations

The water rejoins the river immediately below the falls. Established.

It goes down the pothole, travels a short distance underground, and comes straight back up into the plunge pool below. There is no underground river, no lava tube, and no subterranean journey to Lake Superior. It goes into a hole and comes out again, a few metres away, under the churn where nobody can see it.

Why nothing ever came out. The plunge pool at the bottom is violent. Anything thrown into the kettle is caught in recirculating currents, held in the turbulence, and battered. A ping-pong ball does not sail out intact and float downstream to be spotted. It is held under, broken up, and released eventually in pieces, or not at all.

The absence of emerging objects was never evidence of an underground river. It was evidence of a strong plunge pool, which is exactly what a waterfall produces.

Current status

Later explained. The registry keeps this short record because of what it demonstrates, which is out of all proportion to the size of the case.

For most of a century, people stood at the Devil's Kettle and threw things into it. Ping-pong balls. Dye. Logs. They were, in effect, running an experiment, and the experiment kept returning the same result, and they kept concluding that the result was a mystery.

Nobody put a flow meter in the river.

The measurement took a day. The mystery lasted eighty years, and it lasted because the question everyone was asking, where does the water come out, is a much harder question than the one that settles it, which is is any water actually missing.

Last reviewed: July 2026. Records are provisional. Where the evidence changes, the entry changes. Found an error? Tell us.