Instead of water, sediment from droughts and wildfire is choking U.S. dams

The United States has lost an estimated 8% of its water storage capacity, the equivalent of 25.5 million Olympic-sized swimming pools, according to a study published in Nature Communications. Drought and wildfire conditions across the U.S. have destroyed plants that hold soil in place, resulting in sediment crumbling into reservoirs and leaving less room for water. Nearly half of all U.S. reservoirs are over one-quarter full. 

In Denver, where residents have spent the summer managing emergency drought protocols, a mound of sediment in the Strontia Springs Reservoir has displaced four days’ supply of drinking water. As climate change worsens the flow of sediment, more and more communities will struggle with freshwater displacement. By 2041, wildfires will double sediment accumulation in more than one-third of U.S. watersheds, according to a study by the U.S. Geological Survey.

Hydrologists and dam engineers describe sediment as a slow-motion car wreck: every dam in the U.S. has an estimated lifespan largely based on how long it will take for sediment to build up past manageable levels, Kyle Stock and Kyle Kim write for the LA Times. Aaron Hurst, a geomorphologist who left the Bureau of Reclamation in 2024, said because reservoir outlets are usually close to the bottom, even a dam that is only 15% full of sediment can be rendered inoperable.