Globally, tropical rivers support a greater diversity of anguillid eel species than rivers in temperate regions. Yet, many of these rivers are undergoing hydropower development and basic knowledge of anguillid population and community characteristics is lacking. In the absence of useful information, tropical anguillid eels are in global decline. This study assessed the abundance, taxon richness, and physiological conditions of upstream-migrating juvenile eels in the Poso River, Central Sulawesi, Indonesia. The Poso River flows from Lake Poso to Tomini Bay and contains two hydropower dams, Poso 2 and Poso 1 (the most upstream of the two). Sampling was conducted in the 2025 wet (May–June) and subsequent dry (October) season at four sites along the river, with Site 1 being in the estuary, Site 2 mid-way along the river, Site 3 downstream of Poso 2 dam, and Site 4 upstream between Poso 2 and Poso 1 dams. We analysed eel osmoregulatory markers (Na+, K+, Cl−), energy metabolism indicators (glucose, total protein, triglycerides), and biochemical indicators (BUN, AST) to provide insight into energetic status, physiological condition, and potential recent migratory effort. Four anguillid species were identified: Anguilla celebesensis, A. marmorata, A. interioris, and A. bicolor pacifica. Juvenile eel abundance was greatest in the estuary and declined at upstream sites. Osmoregulatory concentrations (Na+, K+, and Cl−) were generally lower at the dam sites, and total protein was reduced at upstream sites, whereas BUN and AST were higher at sites near the hydropower dams. These results identify the estuary as a primary recruitment zone and the dam reach as an important area for further assessment of anguillid eel movement and river connectivity, with some evidence of spatial differences in osmoregulatory status, energy reserves, and physiological condition. Such data are an essential foundation for designing, testing, and monitoring appropriate connectivity measures for tropical anguillid eels.