In 2020 the Environmental Protection Agency narrowed the definition of "waters of the United States," significantly limiting wetland protection under the Clean Water Act. Current policy debates center on the uncertainty around wetland benefits. We estimate the value of wetlands for flood mitigation across the United States using detailed flood claims and land use data. We find the average hectare of wetland lost between 2001 and 2016 cost society $1,840 annually, and over $8,000 in developed areas. We document significant spatial heterogeneity in wetland benefits, with implications for flood insurance policy and the 50 percent of "isolated" wetlands at risk of losing federal protection.