Protected areas (PAs) are an essential tool for freshwater biodiversity conservation. Given past and expected future global increases in dams and impacts of dams on freshwater ecosystems, we document the number of dams existing or planned within PAs, their history, and the extent of PA downgrading, downsizing, and degazettement (PADDD) proximally caused by dams. Globally, at least 1,249 large dams are located within PAs; two‐thirds (907) were built before PA establishment. Additionally, 14% of planned geolocated hydropower dams (509 dams) are located within PAs. PADDD events have also legalized dam construction within existing PAs. Environmental safeguards should preclude development of dams within or adjacent to PAs and prioritize dams within PAs for possible removal and restoration.

Approximately one-third of long rivers remain free-flowing, and rivers face a range of ongoing and future threats. In response, there is a heightened call for actions to reverse the freshwater biodiversity crisis, including through formal global targets for protection. The Aichi Biodiversity Targets called for the protection of 17% of inland water areas by 2020. Here, we examine the levels and spatial patterns of protection for a specific type of inland water area—rivers designated as free-flowing. Out of a global total of 11.7 million kilometers of rivers, 1.9 million kilometers (16%) are within protected areas and 10.1 million kilometers are classified as free-flowing, with 1.7 M kilometers of the free-flowing kilometers (17%) within protected areas. Thus, at the global level, the proportion of rivers in protected areas is just below the Aichi Target, and the proportion of free-flowing rivers within protected areas equals that target. However, the extent of protection varies widely across river basins, countries, and continents, and many of these geographic units have a level of protection far lower than the target. Further, high discharge mainstem rivers tend to have lower extent of protection. We conclude by reviewing the limitations of measuring river protection by the proportion of river kilometers within protected areas and describe a range of mechanisms that can provide more effective protection. We also propose a set of recommendations for a more comprehensive quantification of global river protection.

The Amazon Basin features a vast network of healthy, free-flowing rivers, which provides habitat for the most biodiverse freshwater fauna of any basin globally. However, existing and future infrastructure developments, including dams, threaten its integrity by diminishing river connectivity, altering flows, or changing sediment regimes, which can impact freshwater species. In this study, we assess critical rivers that need to be maintained as freshwater Bernardo Caldas and Michele L. Thieme are joint first authors.

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