Seymour Narrows is a corridor half a mile wide and two miles long between Discovery Passage and Johnstone Strait. The tide runs through the Narrows at speeds from 12-15 knots with about half an hour of slack tide twice a day.
Since 1875, at least 114 lives have been lost and 120 vessels have been damaged or sunk in these waters. These disasters were mostly due to Ripple Rock which jutted to within 10 feet of the water's surface in the middle of the channel.
The first recorded victim of the Rock was the US gunboat Saranac which sunk in 1875. The last large vessel to run into trouble here was the Canadian ship, William J. Stewart, in the early 1940s, which was holed when it swerved to avoid an oncoming passenger vessel. The most serious loss of life occurred aboard the converted US naval vessel Grappler, which caught fire at the entrance to the narrows in 1883. About 77 people died, most of them Chinese bound for coastal canneries.
In 1958, after many unsuccessful attempts to remove the rock, 1,400 tons of high explosives were placed at the end of a tunnel under the narrows and the top 40 feet of the rock were demolished. It was the largest non-nuclear explosion in the world up to that date. Removal of the rock had been a politically sensitive issue because some feared it would trigger an earthquake or tidal wave, neither of which happened. Others opposed the blast because they believed Ripple Rock could serve as the base for a pillar to support a bridge across Seymour Narrows which would have been a major link from the BC mainland to Vancouver Island.