A freshwater resilient and connected network to sustain biodiversity under a changing climate.

Over the last century, the integrity of streams and lakes in the U.S. has deteriorated. Our river networks are fragmented by thousands of dams hindering movement and adaptation. Water diversions, groundwater withdrawals, and habitat degradation have depleted flows and altered hydrology. Now climate change is altering precipitation patterns and temperature regimes, sending freshwater species into rapid decline. To address this crisis, The Nature Conservancy (TNC), working with 66 freshwater conservationists representing 44 states, mapped the characteristics that impart resilience to freshwater systems and identified a representative network that, if conserved and restored, could theoretically sustain the nation's aquatic biodiversity. Key attributes of resilience included connectivity, condition, water availability, and naturalness of flow. Each attribute was assessed individually, and the results were combined into a resilience score for every small watershed (HUC-12). We overlaid the results with 91 spatial freshwater biodiversity assessments to identify a network that meets criteria for representation, resilience, connectivity, and biodiversity: what we have termed a 'freshwater resilient and connected network.' The network covers 35% of the conterminous U.S. and separates into 19% scoring as resilient and 16% as restorable (i.e., average resilience with one below-average factor). It includes 67% of recognized biodiversity areas, 75% of free-flowing rivers, and at least 30% of every freshwater ecoregion except one. Current conservation of the network distributes as 6% protected and resilient, 2% protected and restorable, 13% unprotected and resilient, and 14% unprotected and restorable. The results form a foundation for sustaining diverse and adaptive freshwater systems.