To protect against erosion and the buffeting of ocean waves, people living in coastal communities often build hard structures like sea walls and bulkheads. As a result, nearly 14% of the U.S. shoreline is now coated in concrete, say researchers who recently conducted the first nationwide survey of artificial coastal infrastructure. Using data collected by the National Oceanic and Atmospheric Administration (NOAA), the researchers found that at least 22,842 kilometers of the nation’s ocean, estuary, bay, and tidal river shores are now “hardened” or artificially armored against the waves. Hot spots include Boston, San Francisco, and many parts of Florida. If current trends continue, the researchers—who presented their findings at the Ecological Society of America’s annual meeting last week—project that up to one-third of the nation’s coastline could be hardened by 2100. The fastest rates of fortification seem likely to be in the rapidly developing areas of the south Atlantic and Gulf coasts. But such trends are troubling, the scientists say, because hard structures not only protect shorelines (and the property values that go with them), but they also bounce waves’ energy seaward, where the water can scour beaches and destroy tidal marshes that are not protected by concrete, ultimately making coastal areas more vulnerable to storms. The researchers hope their study encourages landowners and government agencies to quit piling on the concrete in favor of “living shorelines,” natural barriers that prevent erosion and protect coastal ecosystems at the same time.