Following the unintentional introduction of the freshwater mussel Sinanodonta pacifica into Indonesia, it dispersed rapidly. The life cycle and reproductive characteristics of this species throughout Indonesia are poorly known. This information is required to manage the species and mitigate against any negative effects that it might have on native ecosystems. We firstly report on the reproductive biology of S. pacifica by combined temporal monitoring, histological investigation, and light and scanning electron microscopy, and relate mussel densities, and their reproductive and embryological stages, to environmental variables at five sites in West Java from 67 to 1,580 m above sea level. Sinanodonta pacifica is protandrous and can spawn eggs and brood larvae throughout the year, with spawning peaks in the early rainy season from September to December. Mussels from midland sites brood 4.1–8.9‐fold more glochidia than those from lowland or highland sites; highland and lowland sites produce 3.1–4.3‐fold more hermaphrodites than midland sites. High levels of suspended solids and low chlorophyll‐a concentrations contribute to a higher proportion of hermaphrodites and a decrease in glochidia production. Low mussel densities and an unbalanced sex ratio also contribute to increased proportions of hermaphrodites, and reduced glochidia production. These results improve our understanding of how S. pacifica recruits across elevations, and how population growth might threaten native species and natural ecosystems. Management involving periodic harvesting of mussels to control population size and promotion of economic benefits from pearl production is proposed.