Samuel de Champlain anchored his first habitation at the foot of Cap Diamant in 1608, choosing the site because the St. Lawrence narrows to less than one kilometre at this point — Kebec in Algonquin, meaning "where the river narrows." Four centuries later, that same constriction defines every boat ride Quebec City offers, as vessels navigate the channel between the Laurentian highlands and the southern shore, tracing the route that brought explorers, merchants, and immigrants into the heart of a continent. The St. Lawrence at Quebec is a tidal river. Twice daily, the Atlantic pushes upstream, raising water levels by up to five metres and reversing the current for hours at a stretch. This tidal bore shapes departure schedules and defines the cruising experience — morning sailings ride the flood tide upriver toward Montmorency Falls, while afternoon departures drift downstream on the ebb past Grosse-Île and the Île d'Orléans archipelago. The interplay of fresh and salt water creates a brackish transition zone that supports beluga whales downstream and Atlantic sturgeon in the estuary, species visitors occasionally spot from the deck rails. The working waterfront remains visible from every sightseeing cruise. Grain elevators and container terminals share the harbour with the Agnico Eagle cruise terminal and the Quai Chouinard departure docks. The Pont de Québec — the longest cantilever bridge span in the world at 549 metres — frames the western approach, its riveted steel trusses a monument to early 20th-century engineering and the site of two catastrophic collapses during construction. Zodiac operators thread beneath its shadow, close enough to study the lattice work that claimed 88 lives before the span opened in 1919. Every St. Lawrence River cruise in Quebec passes infrastructure that preceded the city's UNESCO designation, reminders that this was a commercial artery before it became a tourist corridor.