Spatial and temporal heterogeneity, or messiness, is a broadly desirable characteristic of river corridors and an indicator of many of the geomorphic processes that sustain fluvial ecosystems. However, quantifying geomorphic heterogeneity is complicated by a lack of consistent metrics, classification schemas for dividing the river corridor into the patches that form the basis for those metrics, and guidance on interpreting metrics. Drawing from both geomorphic and landscape ecology concepts, we offer ideas and guidance intended to help investigators, from researchers to restoration practitioners, more effectively and reliably use heterogeneity to describe river corridor processes and characteristics. We define geomorphic heterogeneity both spatially and temporally. Spatially, heterogeneity can be described by diversity, or the evenness and richness of geomorphic units, and spatial configuration, or the arrangement and shape of geomorphic units. Temporally, heterogeneity can be described by turnover rate, or the rate of change of geomorphic units. Interpretation of heterogeneity metrics depends integrally on the definition of the geomorphic unit schema on which metrics are based. Contextual information, such as measurements of process space (i.e., how much room a river has to move), disturbance frequency, and geomorphic trajectory, can also be key to interpreting measurements of heterogeneity. Geomorphic applications of heterogeneity require carefully defined geomorphic unit schemas that reflect processes and characteristics of interest, robust metrics of heterogeneity whose meaning is appropriate to the question at hand, and interpretation of those metrics based on the context of expected geomorphic processes and the disturbance regime.