Guaíra Falls, Submerged waterfall site on the Paraná River, Guaíra, Brazil and Salto del Guairá, Paraguay

The Guaíra Falls were a series of immense waterfalls on the Paraná River, comprising 18 cataracts clustered in seven groups—hence the Portuguese name Sete Quedas. At the head of the falls, the river narrowed from about 380 m to 60 m, and the total height was approximately 114 m, with the largest individual cataract 40 m high. The falls ceased to exist in 1982 when they were submerged by the Itaipu Dam reservoir.

The falls lay on the Paraná border until the 1966 Iguaçu Act set their submersion for the Itaipu hydroelectric project, formalized by a 1973 bilateral treaty that also settled the frontier dispute. Brazil's Sete Quedas National Park, created in 1961, was abolished in 1981. Reservoir filling began on 13 October 1982 and submerged the falls within 14 days, by 27 October.

The name Guaíra comes from Tupi-Guarani kuaira, "the impassable, beyond which one cannot pass", as recorded in Silveira Bueno's Tupi-Guarani vocabulary. The falls were the only waterfalls in the world visited from above, via suspended bridges, including the Presidente Roosevelt bridge leading to Salto 19. Before the flooding, hundreds of people held a quarup, an indigenous ritual of remembrance for the dead, in memory of the falls.

The falls no longer exist: since 27 October 1982 they lie under the Itaipu reservoir, formed after the Paraná rose during the rainy season and the diversion canal was closed on 13 October 1982. In dry years, when several intakes of the Itaipu plant operate at once, part of one cataract and many of the rocks re-emerge; this happened in November–January 2000/2001 and November–December 2012 and January 2013. The former falls stood at the border's fifth drop, near Guaíra on the Brazilian side and Salto del Guairá on the Paraguayan side.

The falls were the only waterfalls in the world where visitors could walk over the top of the cataracts on suspended footbridges. One of these, the Presidente Roosevelt bridge leading to Salto 19, collapsed on 17 January 1982 under the crowds rushing to see the falls before the reservoir rose; 32 people died and six were saved by fishermen from Guaíra.