The Lower Sesan 2 Dam (LS2) is the largest and most controversial hydropower dam ever developed in Cambodia. The 400 megawatt-capacity project, which blocks both the Sesan and Srepok rivers in Stung Treng province, northeastern Cambodia, was first envisioned in 1998, although the project was only completed in 2018. LS2 was initially an Electricité du Viet Nam (EVN) project. Later, however, with strong Chinese government support, a Chinese company, Hydrolancang International Energy Company, took over the Vietnamese share in the project, with EVN holding just a 10 per cent stake, and the Royal Group, a Cambodian company, holding a 39 per cent share. The LS2 was ultimately developed as a Belt and Road Initiative (BRI) infrastructure, with its own political aspects. This article considers the relationship between LS2 and sacred spaces of rural ethnic Lao people, including how spirit mediums and the associated belief systems of local people have been impacted by LS2. We take a feminist political ecology approach to this study, as female spirit mediums have contested the LS2 since before its construction began and have also been directly affected by the dam. They have also served as important shadow infrastructure. We argue that, apart from having potentially important material impacts, dams such as LS2 also serve to alter nature-society relations through variously affecting spirit mediums, their practices, and beliefs associated with spirits.