Aquatic communities were characterized at fifteen ephemeral stream sites within the Santa Cruz River, Rio Puerco, and Huerfano River watersheds, located respectively in Arizona, New Mexico, and Colorado.  One purpose of the study was to provide preliminary data on succession patterns of aquatic taxa into these ecosystems (both with and without upstream sources of potential colonizers) within the arid southwest as a function of flow duration.  Sampling of macroinvertebrate populations was conducted at each site following a precipitation event and continued daily until surface water was no longer present.  Results of this study demonstrate limited succession patterns, with few taxa remaining present for extended periods of time.  Most taxa collected had aerially dispersing life stages, and their presence at these sites is likely a result of random processes.  Patterns in taxa richness was generally associated with duration of flow, which varied among the watersheds, apparently due to difference in substrate water retention.  Examination of life histories characteristics suggested that few of the colonizers would  complete their life cycle within the short time span of water presence in these ephemeral streams.