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The Reversing Falls are a series of rapids on the Saint John River located in Saint John, New Brunswick, Canada, where the river runs through a narrow gorge before emptying into the Bay of Fundy. The phenomenon of the Reversing Falls is caused by the tremendous rise and fall of the tides of the Bay of Fundy, which are the highest in the world. As the bay tides begin to rise, they slow the course of the river and finally stop the river's flow completely. This short period of complete calm is called slack tide. It is only at this time that boats are able to navigate the Falls. Shortly after this slack tide the bay tides become higher than the river level and slowly, at first, the river begins to flow upstream. As the bay tides continue to rise, the reverse flow gradually increases and the rapids begin to form, reaching their peak at high tide. The effect of this reversal is felt upstream as far as Fredericton, more than 80 miles inland. At this point the tidal waters are actually 14 ½ feet higher than the river
