The St. Lawrence meets the Saguenay at Tadoussac over an underwater sill barely 20 metres deep, while the estuary beyond it plunges past 300. That single ledge of rock explains everything. Tidal currents drive cold, nutrient-rich water upward against the sill, seeding vast blooms of krill and capelin in the narrow channel off Pointe de l'Islet. Whales have fed here for as long as anyone has kept records. Basque whalers worked these waters in the sixteenth century. In 1600, Pierre de Chauvin raised a fur-trading post at Tadoussac — the oldest surviving European settlement north of Mexico still inhabited, and older than Québec City by eight years. The Innu called the place Totouskak, a word for breasts, after the rounded hills above the bay. For three centuries the village lived on pelts, then on timber, then on the steamships that carried Victorian tourists down from Montréal to the red-roofed Hôtel Tadoussac. The whales were scenery, then cargo, then a science, then an economy. A tadoussac charlevoix whale watching tour today follows sea lanes that fur canoes once crossed. Protection came late. The Saguenay–St. Lawrence Marine Park, created in 1998, was Canada's first park to protect a marine environment alone, jointly managed by the federal and Québec governments across 1,245 square kilometres. Its rules govern approach distances, engine speeds and vessel numbers, and they exist because the beluga population here — an isolated, endangered group of roughly 1,850 animals, marooned since the last glaciation — cannot absorb disturbance. Thirteen cetacean species pass through. Minke and fin whales are near-constant in summer. Humpbacks breach along the north shore. Blue whales, the largest animals ever to have lived, feed in the deep channel most years, and the estuary is one of the few reliable places on Earth to see them from a small boat. Across the fjord, Charlevoix supplies the geology. The region sits inside a 56-kilometre impact crater carved roughly 450 million years ago; its terraced farmland and abrupt cliffs are the eroded rim. UNESCO designated Charlevoix a World Biosphere Reserve in 1988. Zodiac operators, larger cruise vessels and croisière aux baleines Tadoussac departures all leave from the same marina at the river's edge, where the tide can swing four metres in a day and the water rarely climbs above 10°C in August. What makes the estuary unusual is not the number of whales but the intimacy of the meeting. The feeding grounds sit within a few nautical miles of shore. Marine biologists from the Groupe de recherche et d'éducation sur les mammifères marins, based in the village since 1985, have photo-identified individual humpbacks and blue whales here across four decades, tracking the same dorsal fins year after year. Visitors on a tadoussac charlevoix whale watching tour tour share the water with that research fleet, and the Tadoussac whale watching boat tour fleet operates under the same distance limits the scientists helped write.