Their name comes from the Guarani or Tupi words y (IPA:[ɨ]) (water) and ûasú (IPA:[wa'su]) (big). Legend has it that a god planned to marry a beautiful aborigine named Naipí, who fled with her mortal lover Tarobá in a canoe. In rage, the god sliced the river creating the waterfalls, condemning the lovers to an eternal fall. The first European to find the falls was the Spanish Conquistador Álvar Núñez Cabeza de Vaca in 1541, after whom one of the falls in the Argentine side is named. The falls were rediscovered by Boselli at the end of the nineteenth century, and one of the Argentinian falls is named after him.
The waterfall system consists of 275 falls along 2.7 kilometers (1.67 miles) of the Iguazu River. Position is at Latitude (DMS): 25° 40' 60 S ,Longitude (DMS): 54° 25' 60 W . Some of the individual falls are up to 82 meters (269 ft) in height, though the majority are about 64 metres (210 ft). The Garganta del Diablo (Devil's Throat in English; Garganta do Diabo in Portuguese), a U-shaped 150-metre-wide and 700-metre-long (490 by 2300 feet) cliff, is the most impressive of all, and marks the border between Argentina and Brazil. Two thirds of the falls are within Argentine territory. About 900 metres of the 2.7-kilometer length does not have water flowing over it. The edge of the basalt cap recedes only 3 mm per year. The water of the lower Iguazu collects in a canyon that drains into the Rio Parana in Argentina, shortly downstream from the Itaipu dam.
The falls can be reached from the two main towns on either side of the falls: Foz do Iguaçu in the Brazilian state of Paraná, and Puerto Iguazú in the Argentine province of Misiones as well as from Ciudad del Este (Paraguay) on the other side of the Parana river from Foz do Iguaçu. The falls are shared by the Iguazú National Park (Argentina) and Iguaçu National Park (Brazil). These parks were designated UNESCO World Heritage Sites in 1984 and 1986, respectively.
On the Brazilian side there is a long walkway along the canyon with an extension to the lower base of the “Garganta del Diablo”. The Argentian access is facilitated by the Tren Ecológico de la Selva (Rainforest Ecological Train), which brings visitors to different walkways. The “Paseo Garganta del Diablo” is a one kilometer long way to bring the visitor directly over the falls of the “Garganta del Diablo”. Other walkways allow access to the elongated stretch of falls on the Argentinian side and to the ferry that connects to the San Martin island.
The fall area provides opportunities for water sports and rock climbing.
Upon seeing Iguaçu, First Lady Eleanor Roosevelt reportedly exclaimed "Poor Niagara!" Vastly larger than North America's Niagara Falls, Iguaçu is rivaled only by Southern Africa's Victoria Falls which separates Zambia and Zimbabwe (this is excluding extremely large rapid-like falls such as the Boyoma Falls). Whilst Iguazu is wider because it is split into about 270 discrete falls and large islands, Victoria is the largest curtain of water in the world, at over a 1600 m wide and over 100 m (350 ft) in height (in low flow Victoria is split into five by islands; in high flow it can be uninterrupted).
The water falling over Iguazu in peak flow has a surface area of about 40 ha (1.3 million ft²) whilst Victoria in peak flow has a surface area of over 55 ha (1.8 million ft²). By comparison, Niagara has a surface area of under 18.3 ha (600,000 ft²). Victoria's annual peak flow is also greater than Iguazu's annual peak—9 100 m³/s versus 6 500—though in times of extreme flood the two have recorded very similar maximum water discharge (well in excess of 12 000 m³/s). Niagara's annual peak flow is about 2 800 m³/s, although an all-time peak of 6 800 has been recorded. Iguazu and Victoria fluctuate more greatly in their flow rate. Mist rises between 30 and 150 m (100 and 500 ft) from Iguazu's Garganta do Diabo, and over 300 m (1,000 ft) above Victoria (sometimes over 600 m).
Iguazu, however, affords better views and walkways and its shape allows for spectacular vistas. At one point a person can stand and be surrounded by 260 degrees of waterfalls. The Garganta do Diabo has water pouring into it from three sides. Likewise, because Iguazu is split into many relatively small falls, one can view these a portion at a time. Victoria does not allow this, as it is essentially one waterfall that falls into a canyon and is too immense to appreciate at once (except from the air). As of July 24, 2006 a severe drought in South America had caused the river feeding the falls to become parched, reducing the amount of water flowing over the falls to 300 m³ (80,000 gallons) per second, down from the normal flow of 1,300 m³/s to 1,500 m³/s (350,000 to 400,000 ga/s). By early December, the flow was spectacular again, according to visiting tourists. This was unusual, as normally dry periods last only a few weeks.