They were deadly, destructive and came with little warning. Here’s what to know about the biggest floods in U.S. history.
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Black Hills flood
Date: June 9–10, 1972
Location: Rapid City, South Dakota
This 1972 weather event is the biggest flood to hit the U.S. in the last 100 years. In the eastern Black Hills of South Dakota near Rapid City, a stationary group of thunderstorms began around 5 p.m. on June 9, 1972, and produced record rainfall. Roughly two hours later, a flash-flood warning was issued for the area. According to the U.S. Geological Survey (USGS), nearly 15 inches of rain fell in about six hours, with more than 10 inches of rain falling over a 60-square-mile area.
The flood peaked between 10:30 p.m. on June 9 and 1 a.m. on June 10. From there, the events unfolded like something out of a disaster movie. By 8 p.m., two smaller dams broke, but the most destruction occurred when the Canyon Lake Dam became clogged with debris and failed around 10:45 p.m., sending floodwaters rushing through Rapid City—the hardest-hit location in the flood.
At least 238 people died in the Black Hills flood, and another 3,057 were injured. The USGS estimates that the total damage from the flood exceeded $160 million, after the flood destroyed homes, vehicles, businesses and bridges.
Today, it’s even more common for cities to experience flash floods. “Rain-driven urban/flash flooding is increasing in many areas as heavier downpours meet more pavement and less natural drainage,” Clark says. The idea that floods can only happen around rivers or on the coasts is a weather myth that often leaves people unprepared and at risk.
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Republican River flood
Date: May 31–June 1, 1935
Location: Eastern Colorado and southwestern Nebraska
Picture it: May 1935 in the Dust Bowl, during one of the greatest droughts the Great Plains had ever seen. About halfway through the month, it began to rain, with severe thunderstorms sweeping through eastern Colorado, western Kansas and southwest Nebraska.
Then, on the night of May 30, a particularly heavy storm in the area caused the Republican River to flood and then rise quickly. The combination of “saturated soil, the prolonged heavy rain, and the parallel movement of the storms along the Republican River Basin created an extreme flooding event,” devastating communities along the river, according to the NWS. To make matters worse, a dust storm swept through McCook, Nebraska, at the peak of the flood.
Fresh water was moving at about 4 mph, exerting a force of approximately 66 pounds per foot on anything it encountered, creating dangerous conditions. “Even shallow, fast-moving water can knock a person off their feet or lift and float a car,” Abshire says.
Between 159 and 168 people died in the Republican River flood. Homes, other buildings, roads, bridges, railroads and communication lines were damaged, costing an estimated $26 million.
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Virginia flash floods from Hurricane Camille
Date: Aug. 19–20, 1969
Location: Nelson County, Virginia
On Aug. 17, 1969, Hurricane Camille slammed into the coast of Mississippi—one of only a few Category 5 storms to make landfall in the United States since recordkeeping began. Although the storm weakened to a tropical depression by the time it reached Virginia on Aug. 19, it brought widespread torrential rains that caused massive flash flooding. In an eight-hour period, 12 to 14 inches of rain fell in the mountains of the state, with amounts exceeding 27 inches in one area.
Because telephone lines were down because of the storm, people were unable to warn others about the rising waters. The Virginia flash flooding claimed the lives of 153 people and caused $116 million in damages. More than 100 bridges were swept away in the flood, which left only one highway in Nelson County intact. In addition to homes and businesses, many acres of farmland were ravaged in the floods, as was local industrial production.
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Big Thompson River flood
Date: July 31, 1976
Location: Larimer and Weld Counties, Colorado
When thunderstorms stalled near Estes Park, Colorado, on the evening of July 31, 1976, no one was prepared for what was to come. A year’s worth of rain fell in the span of about an hour, and ultimately, the slow-moving storm dumped 12 to 14 inches of rain on the area.
But things were about to get worse. Around 10:30 p.m., a massive wave of water nearly 20 feet tall passed through the Big Thompson Canyon, wiping away everything in its path. “In steep terrain like mountains, canyons and hilly regions, water funnels into narrow channels and can rise very quickly, leaving little time or space to escape,” Abshire explains.
The Big Thompson River flood left 144 people dead and more than 250 injured. It caused more than $35 million in total damages and destroyed at least 418 homes. While some homes were eventually rebuilt, many weren’t, as people wanted to avoid living in a flood plain. Additionally, more than 400 vehicles in the area were carried off the roads and crashed down into the canyon.
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Central Texas floods
Date: July 4–5, 2025
Location: 20 counties in central Texas
The fifth-deadliest flash flood in U.S. history took place in July 2025 in central Texas, also called Texas Hill Country. On the night of July 3, slow-moving thunderstorms—the remnants of Tropical Storm Barry—dumped around 18 inches of rain in just a few hours. This resulted in a wall of water surging through Kerr County’s Guadalupe River basin at around 4 a.m., catching many people off guard. At one point, the Guadalupe River rose about 26 feet in 45 minutes.
Hundreds of emergency rescues took place over the 4th of July weekend, but not everyone was saved. The flood hit Camp Mystic, an all-girls summer camp, especially hard, leaving 27 campers and counselors dead. Overall, the floods claimed at least 141 lives.
The cost of the damage is estimated to range from $18 billion to $22 billion, thanks to the flood washing away homes, businesses and large trees, as well as damaging roads.
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What was the biggest flood in U.S. history?
The biggest flood ever to hit the United States lies outside of our 100-year metric. That dubious distinction goes to the Johnstown Flood, also known as the Great Flood of 1889, which swept through Johnstown, Pennsylvania, on May 31 of that year. This flash flood killed somewhere between 2,209 and 3,188 people, destroyed more than 1,600 homes and caused an estimated $17 million in property damage.
Heavy rains on May 31, 1889, resulted in the catastrophic failure of the South Fork Dam on the Little Conemaugh River, roughly 14 miles upstream from Johnstown. At around 4 p.m. that day, a nearly 35-foot wave of water and debris surged through the mill town, completely destroying 4 square miles of the downtown area. In some places, the debris caught on fire, adding to the dangerous conditions.
Along with the Johnstown Flood, here are some of the other deadliest flash floods from more than a century ago:
- The Heppner, Oregon, flood in 1903: 247–251 deaths
- The Central Texas tropical depression in 1921: 224-plus deaths
- The Lehigh River Valley, Pennsylvania, flood: 1862: about 150 deaths
About the experts
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Why trust us
At Reader’s Digest, we’re committed to producing high-quality content by writers with expertise and experience in their field in consultation with relevant, qualified experts. We rely on reputable primary sources, including government and professional organizations and academic institutions as well as our writers’ personal experiences where appropriate. For this piece on the biggest floods ever to hit the United States, Elizabeth Yuko, PhD, tapped her experience as a professor and longtime journalist who often covers history and knowledge for Reader’s Digest. We verify all facts and data, back them with credible sourcing and revisit them over time to ensure they remain accurate and up to date. Read more about our team, our contributors and our editorial policies.
Sources:
- Kate Abshire, National Weather Service’s Flash Flood Services lead; email interview, Sept. 24, 2025
- Ed Clark, director of the National Oceanic and Atmospheric Administration’s National Water Center; email interview, Sept. 24, 2025
- Yale Climate Connections: “The deadliest floods in U.S. history”
- National Weather Service: “Severe Weather Awareness Week—Flash Flood Safety”
- National Weather Service: “History of the National Weather Service”
- Wayne Blanchard: “Deadliest American Disasters and Large Loss-of-Life Events”
- U.S. Geological Survey: “The Black Hills-Rapid City flood of June 9-10, 1972: A description of the storm and flood”
- National Weather Service: “The Black Hills Flood of 1972”
- National Weather Service: “Republican River Flood of 1935”
- Virginia Humanities: “Hurricane Camille (August 1969)”
- U.S. Geological Survey: “Storm and flood of July 31-August 1, 1976, in the Big Thompson River and Cache la Poudre River basins, Larimer and Weld Counties, Colorado”
- United Nations: “‘Very limited time to react’: Texas flash floods expose challenges in early warning”
- Johnstown Flood Museum: “Statistics about the great disaster”
