The Niagara River and all of humanity are at peak flow in Niagara Falls from May through mid-October. The hot summer months are perfectly suited for exploring the wet-and-wild attractions in Niagara Falls State Park, as well as enjoying the many outdoor pursuits in northwestern New York. Prices are highest during these months, as well, but it’s the ideal time to check out Niagara Falls' historic outposts on the bluffs of Lake Ontario and around the Erie Canal. The start of the high season is a little soft—depending on how warm it is, crowds can start heading north as early as mid-April.
Technically speaking Niagara Falls has two shoulder seasons: fall and spring. Once the weather turns really nippy, usually after Halloween (Oct. 31), traffic drops precipitously. It doesn’t help that during the slow months the local hydro-power company siphons off half of the water flow from Niagara Falls. All that makes for a listless-looking natural wonder, but crowds still come well into November as long as temperatures aren’t routinely at freezing or below (and that does happen this far north). Spring starts at some point mid-March, and usually lasts a muddy two weeks. Since you’re going to get wet anyway at Niagara Falls, don’t let a little rain dissuade you from visiting. Hotel rates will be lower than peak season, but still higher then you’ll find in mid-winter.