 A few months before the reservoir was filled, 80 people died when an overcrowded bridge overlooking the falls collapsed, as tourists sought a last glimpse of the falls.The Guaíra Falls was an effective barrier that separated freshwater species in the upper Paraná basin (with its many endemics) from species found below it, and the two are recognized as different ecoregions.After the falls disappeared, many species formerly restricted to one of these areas have been able to invade the other, causing problems typically associated with introduced species.