The Reversing Rapids is a unique phenomenon created by the collision of the Bay of Fundy's monstrous tides and the mighty St. John River. At low tide, the Saint John River, which runs for 724 km (450 mi.) through New Brunswick, empties into the Bay through a narrow rocky gorge. Near Fallsview Park, an underwater ledge 11 m (36 ft.) below the surface causes a series of rapids and whirlpools. At this point the tidal waters are 4.4 m (14.5 ft.) lower than the river level. As the Bay tides begin to rise they slow the river current to a stop and for 20 minutes a rest period called slack tide allows boats to navigate the rapids. The Bay's tides continue to rise, their powerful force gradually reversing the flow of the river and the rapids begin to form again, reaching their peak at high tide. The water rises up to 4.4 m (14.5 ft.) higher than the river.
