Waterfalls are among the most striking scenes one can find in nature: vast volumes of water plunging over a rocky abyss, producing clouds of vapour and a roar that can be heard for miles. For most people in North America, the famed Niagara Falls, lying between Ontario (Canada) and New York, are the greatest recognizable waterfalls. However, they are not the largest in the world, or even in North America. Technically, the widest major waterfall is Iguazu Falls, on the Iguazu river between Brazil and Argentina.
There are essentially three ways to measure the size of waterfalls: by their height, by the volume of water which pours over them in an average period, and by their width. No single waterfall is greatest by more than one of these indicators. To complicate matters further, if one considers a waterfall to be any system in which water falls from a higher area of a river to a noticeably and suddenly lower area, than the massive Boyoma falls in the Congo are easily the largest, even though at any one location Boyoma does not drop more than a few feet at the time (and therefore is hardly the sort of waterfall which attracts either tourists or record-seekers).
In terms of comparison, Niagara Falls, at about 170 feet high and about 3950 feet wide, features an impressive volume of water but is actually comparatively puny compared to some giant falls elsewhere in the world. The famed Victoria Falls in Zimbabwe are much larger, at 360 feet high and 5600 feet wide.
However, in terms of width alone, the world record belongs to the vast Iguazu Falls in South America (visible here). The name is drawn from the indigenous Guarani words for "big water" and, according to local mythology, was created when a spurned god sliced the river in half to separate a woman he was attracted to from her human lover. The conquering Spaniards reached the falls in the 1500s, but subsequently lost the location; it was not visited by another European traveller (or at least one who kept a journal of the occasion) until the 1800s.
The Iguazu Falls actually consist of nearly 300 separate falls spanning over one mile in length along the river, with the largest and most striking being the Devil's Throat fall. Overall the falls span a total distance of over 2.5 kilometers (about 1.5 miles), but not all of this span actually has falling water over it. (By way of analogy, the total width of Niagara Falls is also greater than the total width of falling water, because of Goat Island, which lies in the center of the river at the falls.)
The falls are located between Brazil and Argentina, and can be reached from Foz do Iguacu in Brazil, Puerto Iguazu in Argentina, or Ciudad del Este in Paraguay. The Brazilian falls, part of Iguazu National Park, feature a walkway stretching to the Devil's Throat, while the Argentine side, part of Iguacu National Park, includes a train linking several different walkways and trails. The falls themselves are a UNESCO World Heritage Site.