The most famous falls on the continent runs on a 1950 treaty: 100,000 cfs must come over during tourist season daytime hours, half that the rest of the time, with the balance sent to power plants.
April through October, by treaty
Big water window
in a typical year
Flow controlled
What drives it
Niagara River
Climatology
Data on this page
Niagara River is ungauged
NY State Parks
Managed by
their rules govern
Trail status, closures and safety rules belong to each falls' managing agency, named and linked on every page.
The season
What fills Niagara Falls, and when
Niagara is the ultimate flow-controlled falls. Under the 1950 Niagara River Water Diversion Treaty, verified from the International Joint Commission, at least 100,000 cfs must pass over the falls from 8 am to 10 pm between April 1 and September 15 (to 8 pm through October 31), and at least 50,000 cfs at all other times; the rest of the river is diverted for hydropower. Visit in tourist season daytime and you see twice the water of a winter night, by law.
Typical best flow: April through October, by treaty
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What the agency itself says
The park is open year round but attractions are open seasonally.
A flow-controlled falls when the schedule favors it: Shoshone Falls with the spring Snake River coming over the full brink. The dry season photograph of the same falls is the other bookend. “Shoshone Falls near Twin Falls, Idaho” by Frank Schulenburg, CC BY-SA 4.0
Getting there
Access, in the agency's words and ours
Niagara Falls State Park is open year round, per New York State Parks, with attractions like Cave of the Winds operating seasonally and some open in winter. The American Falls, Bridal Veil and Horseshoe Falls all show from the park's overlooks.
The reliable big-water window is April through October, by treaty. Niagara is the ultimate flow-controlled falls. Under the 1950 Niagara River Water Diversion Treaty, verified from the International Joint Commission, at least 100,000 cfs must pass over the falls from 8 am to 10 pm between April 1 and September 15 (to 8 pm through October 31), and at least 50,000 cfs at all other times; the rest of the river is diverted for hydropower. Visit in tourist season daytime and you see twice the water of a winter night, by law.
Niagara River has no USGS gauge near the falls, so the seasonal pattern above is the flow guide for Niagara Falls, and Niagara Falls State Park (New York State Parks) is the source for current conditions on the ground.
Never, the treaty forbids it. What changes is the split: daytime tourist-season flow is roughly double the overnight and winter minimum, so the same falls genuinely is bigger at noon in July than at midnight in January.
Niagara Falls State Park (New York State Parks). Niagara Falls State Park is open year round, per New York State Parks, with attractions like Cave of the Winds operating seasonally and some open in winter. The American Falls, Bridal Veil and Horseshoe Falls all show from the park's overlooks. Trail status, closures and safety rules are theirs, and their page is linked on this one; nothing here overrides what they publish.
Yosemite Falls in May, running on snowmelt that will be gone by late summer. The National Park Service tells visitors the falls can be dry by August, which is why every falls page here starts from its watershed. “Tourists below Yosemite Falls (39832011431)” by Mike McBey, CC BY 2.0
A 215 foot single plunge past 400 foot gorge cliffs near Ithaca, taller than Niagara, biggest with the Finger Lakes spring runoff and thin by late summer.
New York's tallest waterfall by the DEC's own account, a 260 foot two-tier drop in the Catskills painted by the Hudson River School and treated with respect by everyone who reads the DEC's warnings.
Three major falls on the Genesee River in the Grand Canyon of the East, with the flow-setting dam conveniently DOWNSTREAM, so what comes over is the river's own weather.
Places to stay