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A surge channel is a narrow inlet on a rocky shoreline. As waves strike the shore, water fills the channel, and drains out again as the waves retreat. The narrow confines of the channel create powerful currents that reverse themselves rapidly as the water level rises and falls.
Surge channels can range from a few inches across to 10 feet or more. They may create tide pools if the conditions are correct, but the rapid water movement almost always creates a dangerous situation for people or animals that are caught in it. The West Coast Trail on the coast of Vancouver Island, B.C., is famous for its large number of surge channels, some of which are impassable even at low tide and must be crossed inland.