Sustainable development in river basins depends on the balanced management of water, energy, and food resources, which are closely interlinked and often compete for limited supplies. Addressing these interdependencies through a nexus perspective enables more coordinated strategies, reduces resource-use conflicts, and supports long-term resilience. This study presents an indicator-based framework for assessing Water-Energy-Food (WEF) interactions at the basin scale. The framework is structured in three levels: Level 1 analyzes and covers direct two-way relationships between water, energy, and food; Level 2 examines how any two resources jointly influence the third; and Level 3 integrates these results into a single composite index to capture the overall nexus condition. By focusing on biophysical perspective, the framework reduces complexity, remains adaptable across river basins, and facilitates cross-basin comparisons. The framework is applied to the Ping River Basin, Thailand, to demonstrate its utility. Findings point to a downward trend in nexus performance, mainly due to rising agricultural water demand and reduced efficiency in energy provision and water services. Overall, the framework offers a practical decision-support tool for guiding system-based interventions in WEF resource management.