Between Vancouver Island and the Discovery Islands in British Columbia, lies a narrow body of water called Seymour Narrows, which is part of larger strait called Discovery Passage. The Discovery Passage is frequently used by vessels, including cruise ships and freighters, because it enables them to avoid some of the bad weather in the open ocean. The Seymour Narrows, however, has its own hazards. It is very narrow and is known for strong tidal currents. And right in the middle of the strait, below the waters, lurks an underwater mountain called Ripple Rock.
Source: amusingplanet.com