There is a considerable amount of hydropower dam development along the Mekong River. The rationale behind countries’ dam development is based on the premise that these provide long-term economic competitiveness, providing energy for the dams’ lifespans of fifty years or more (Cronin, Eyler & Weatherby, 2016). Despite this, the cumulative effects of cascade dams threaten downstream countries’ water-energy-food security nexus. The purpose of the study is to provide insights into how the future eventualities - the business as usual scenario, worstcase scenario, and the preferred scenario - may unfold by 2040, and the implications on Cambodia. Regarding the methodology, the study employs foresight methodology to create scenario planning. Thirteen experts from all of the Mekong countries were interviewed to form the expert understanding required to map out the scenario. Given the triangulated effects of dam development and climate change, we ask what measures should be taken to circumvent the worstcase scenario in order to achieve the preferred scenario. There are two policy recommendations: reciprocity, and national water security plan for the next 20 years.