The whole Niagara River, from the gauge at Fort Erie, against the water that actually goes over the falls, from the gauge in the gorge below. Everything in between went into the tunnels and conduits to the power plants.
Hover or touch the graph to read any moment. Drag across the strip below it to zoom, or drag the bright window to move it.
The whole river is Environment Canada's gauge on the Niagara River at Fort Erie (02HA013), which measures everything leaving Lake Erie every five minutes. It posts about an hour and a half late, so the newest stretch holds the river at its last reading.
The falls come from NOAA's water-level gauge at Ashland Avenue (9063007), in the gorge below the falls, every six minutes. That spot is the one the 1950 treaty uses for the official falls flow. The official formula from water level to flow isn't published, so this one is fitted to 1,419 daily falls flows from the International Niagara Board of Control's reports for 2021 to 2023. It matches them to a median 3%; read it as plus or minus 5%.
At least 100,000 cfs over the falls from 8 a.m. to 10 p.m. Eastern Standard Time, April 1 to September 15, and 8 a.m. to 8 p.m. from September 16 to October 31. 50,000 cfs at all other times. The dashed line is that minimum; shaded stretches are the treaty's night hours.
How the diverted water divides between New York and Ontario isn't published live. With "Split by country" on, it's shared in the ratio the Board reported for March to August 2023: Robert Moses 56%, Sir Adam Beck 44%. Water also takes a few hours to travel from Fort Erie to the falls, so short swings in the gap are partly timing.