One of the worst calamities to hit the U.S. happened on this date in 1889 — the Johnstown, Pennsylvania Flood. Torrential rains caused a nearby artificial lake to spill over and weaken its earthen dam. When the dam broke, it unleashed 20 million tons of water in a giant wave that roared through Johnstown, killing more than 2,300 people, and destroying the homes of thousands more. The flood remains one of the nation’s most costly, single weather-related disasters. While tornadoes often take more lives, flooding is a constant threat to life. An annual average of 81 deaths occurred in the years between 1986 and 2015. Johnstown has been spared since 1977, when 85 died. Currently, over 20,000 people make Johnstown their home. Profile America is beginning its 20th year as a public service of the U.S. Census Bureau.