High Hazard Dams in America: What You Need to Know

The National Inventory of Dams (NID) tracks approximately 72,949 dams across the United States. Of those, 13,842 are classified as "high hazard" -- meaning that if they were to fail, the resulting flood would likely cause loss of human life.

High hazard does not mean high risk. The classification is based on the downstream consequences of failure, not the likelihood of failure. A brand-new, well-maintained dam in a populated valley is classified as high hazard because of what would happen *if* it failed, even though the probability is extremely low. That said, 7,271 dams are currently rated in poor or unsatisfactory condition, which is where hazard classification becomes most concerning.

The following are among the tallest high-hazard dams in the national inventory. Height is not the only risk factor -- storage volume, downstream population, and condition all matter -- but taller dams generally have greater potential consequences.

Dams are classified into three hazard levels:

• High Hazard: Failure would likely cause loss of life.
• Significant Hazard: Failure could cause significant economic loss, environmental damage, or disruption of lifeline facilities, but loss of life is not expected.
• Low Hazard: Failure would cause minimal damage, primarily limited to the owner's property.

For the complete dam inventory by state, visit our [dams explorer](/dams). To understand how bridge infrastructure compares, see our article on [bridges vs. dams](/blog/bridges-vs-dams-infrastructure).