How much water flows over Niagara Falls?

About 3.16 million gallons (12 million liters) per second go over the falls during peak daytime tourist season. That's the official figure for the combined flow over American Falls and Bridal Veil Falls plus the massive Horseshoe Falls on the Canadian side. But here's the real deal: at night, they slow it down to about 1.4 million gallons per second to save wear and tear and let the hydro plants suck up more water for power. So if you're standing there at 2 AM, you're seeing way less than half the daytime spectacle.

Don't bother asking "how much" like it's a constant number—it's not. The flow is strictly controlled by international treaty between the US and Canada, and they crank it up for tourists during daylight hours from April to October. In winter, the flow is even lower. So if you want the full blast, show up between 8 AM and 8 PM in summer. For the best view, hit the Table Rock observation deck on the Canadian side—it's free, and you can practically feel the mist.