Niagara Falls is the most powerful waterfall in North America, sending close to three thousand tonnes of water over its brink every second. Yet the torrent you watch is only half the river: under a 1950 treaty between Canada and the United States, up to half the Niagara's flow — and three-quarters at night — is diverted through tunnels to power stations before it reaches the edge. It straddles the border, where the river draining Lake Erie into Lake Ontario tips over a limestone cliff left by the last ice age. Horseshoe Falls, largest of the three cataracts, carries about nine-tenths of that water in a curved wall some 57 metres high, while American Falls and Bridal Veil spill alongside it on the American shore. The water keeps cutting the soft rock beneath the ledge, so the falls have crept nearly eleven kilometres upstream in twelve thousand years — a retreat the diversion has now almost stopped.
You hear Niagara long before you see it, a deep, steady roar rising out of the gorge. The widest view is from the Ontario shore, where all three falls line up across the water and boats run straight to the foot of the Horseshoe, into a cloud of spray that soaks everyone aboard and hangs rainbows in the mist when the sun is out. After dark the falls are washed in shifting coloured light, and summer nights bring fireworks; in deep winter the railings and trees crust white with frozen spray and the crowds thin to almost nothing. The signature moment comes at Table Rock, at the very brink, close enough to feel the ground tremble as the river goes over. For all the hotels and towers crowding both banks, the falls stay overwhelming up close — less a view than a force you feel in your chest.