Because of tidal resonance in the funnel-shaped bay, the tides that flow through the channel are very powerful. In one 12-hour tidal cycle, about of water flows in and out of the bay, which is twice as much as the combined total flow of all the rivers of the world over the same period. They are as powerful as 8,000 train engines or 25 million horses. The Annapolis Royal Generating Station, a 20 MW tidal power station on the Annapolis River upstream of Annapolis Royal, was one of the few tidal generating stations in the world, and the only one in North America.