A unique phenomenon created by the collision of the Bay of Fundy and the Saint John River. At low tide the river empties into the bay causing a series of rapids and whirlpools. As tides rise they slow the river current for a brief period called slack tide. The Bay's tides continue to rise, gradually reversing the flow of the river, and rapids form again, peaking at high tide. Tide cycles take about 12.5 hours.