Kilometre-scale jaguar swimming reveals permeable hydropower barriers: implications for conservation in the Cerrado hotspot

Hydropower reservoirs are expanding rapidly across tropical biomes, yet their function as barriers or filters to carnivore movement remains poorly understood. Here, we report the first confirmed long-distance swim by a jaguar (Panthera onca) across an artificial lake and discuss its implications for landscape connectivity. Camera traps around Serra da Mesa Reservoir (Central Brazil; 1,784 km2; 54.4 km3) photographed an adult male on the mainland and later on a forested island. Flank-pattern matching confirmed a 100% identity between records. Geodesic analysis identified two possible routes: a direct 2.48 km crossing or an alternative path involving a stepping-stone islet (1.06 km + 1.27 km). In the absence of evidence for use of the islet, we conservatively adopt the largest continuous water segment--1.27 km--as the minimum distance swum. This represents nearly six times the longest previously verified jaguar swim ({approx} 200 m). The event supports a graduated-resistance framework in which water bodies exceeding 1 km impose high, but not insurmountable, costs to movement. We propose an ordinal aquatic-cost scale (1 = < 300 m; 3 = 300-1,000 m with stepping-stones; 6 = > 1,000 m open water) for use in circuit-based connectivity models. By contrasting this record with predator collapse on > 1 km islands in Lake Guri and with genetic segregation across the Amazon River, we demonstrate that aquatic permeability is strongly context-dependent. Incorporating rare but consequential swims into environmental impact assessments will improve corridor design and better inform hydropower licensing throughout the jaguars range. Highligts- Extends the longest recorded jaguar swim by almost six times. - Demonstrates that reservoirs act as costly filters rather than absolute barriers for large carnivores. - Introduces an ordinal aquatic-cost scale to enhance connectivity models. - Informs hydropower impact assessments and the design of amphibious corridors for mammal conservation.