Overview

• A Nature Communications paper released in July 2025 finds a steady rise in dams exhibiting critical overtopping probabilities based on data from 33 sites dating back to 1973.
• Of the 33 dams analyzed, 30 meet international criteria as large dams and 31 are designated high hazard by FEMA, signaling potential loss of life if failures occur.
• Canyon, Kanopolis, Milford, Somerville, Whiskeytown and Whitney dams emerged as the six highest-risk sites, all located above major downstream cities in Texas, Kansas and California.
• Overtopping now accounts for about 34 percent of US dam failures and the American Society of Civil Engineers’ 2025 report card assigns the nation’s dams a D+ grade, highlighting the scale of needed investments.
• The study offers dam managers a data-driven basis for updating emergency action plans and guides policymakers in prioritizing targeted rehabilitation and spillway upgrades.