The narrows take their name from Rear Admiral Sir George Francis Seymour, who commanded the Royal Navy's Pacific Station from 1844 to 1848. Captain George Vancouver, who had sailed these waters half a century earlier, offered a less diplomatic assessment, calling them "one of the vilest stretches of water in the world." The name has a certain irony -- Seymour himself never had to navigate the passage that bears his name, while the mariners who did, year after year, might have preferred to call it something less dignified. The five-kilometre stretch begins about 18 kilometres from the southern end of Discovery Passage, where it enters the Georgia Strait near Campbell River.

For most of its length, Seymour Narrows is about 750 metres wide -- a bottleneck in Discovery Passage, which otherwise averages two kilometres across. Tidal currents through this constriction regularly reach 15 knots, fast enough to overpower many vessels and produce whirlpools, standing waves, and violent eddies visible from the air. The current reverses with each tide change, and the transition periods are the only windows when safe passage is practical for most ships. Even modern cargo vessels and cruise ships time their transits to slack tide. The narrows mark the northern boundary of the Salish Sea, the vast inland water system that includes the Strait of Georgia, Puget Sound, and the Strait of Juan de Fuca.

As if the currents were not hazardous enough, Seymour Narrows also contained Ripple Rock, a submerged twin-peaked mountain that sat just nine feet below the surface at low tide. The rock sank 119 vessels and killed 114 people between 1875 and 1958. The USS Saranac, a sidewheel steamer, was among the first recorded victims, striking the rock while heading north to Alaska. Multiple attempts to demolish it from the surface failed, defeated by the same currents that made the rock so dangerous. In 1958, after 27 months of tunneling from nearby Maud Island, engineers detonated 1,375 tons of explosive beneath the peaks, dropping them at least 45 feet below the surface. The blast, broadcast live on Canadian television, was the largest planned non-nuclear explosion in North American history.

Removing Ripple Rock did not tame Seymour Narrows. In March 1981, the freighter Star Philippine ran aground here, a reminder that the channel's dangers are permanent features of its geography, not artifacts of a single obstacle. The tidal forces that drive water through the narrows are a function of the enormous volume difference between the Strait of Georgia and Johnstone Strait -- water sloshing between two reservoirs of different heights through a geological pinch point. No amount of engineering can change that equation. Mariners still consult tide tables before entering, and the Canadian Coast Guard monitors traffic through the passage. The Campbell River Museum screens footage of the 1958 Ripple Rock explosion for visitors, a reminder of the one problem that could be solved -- and the many that remain.