Applications of HEC-EFM focus on aquatic habitat and land-water interactions inside the maximum inundated area associated with a river, wetland, or reservoir. Within this domain, the software is capable of testing a diverse and extensive array of management scenarios and ecological relationships. The software relies wholly on the user to define which aspects of the ecosystem are of interest (e.g., fish, vegetation, benthic macroinvertebrates), how those are to be investigated (e.g., at a single diagnostic location, for multiple locations, for many spatial areas), and which hydrologic, operational, or restoration scenarios are considered (e.g., climate change, reservoir releases, channel manipulation). This flexibility in focus, scale, and scenario is an important and defining aspect of HEC-EFM. It is also difficult to fully appreciate.