Algal cover (index), density (individuals/cm2) and biovolume (um3/cm2) for diatoms (species and genus-levels) and soft-bodied taxa (genus-level) and environmental data (hydrology, geomorphology, macroinvertebrate, physicochemical, watershed) from 508 samples across 22 ephemeral, 37 intermittent, and 51 perennial reaches distributed along 31 forested headwater streams within 4 ecoregions in the contiguous United States. Citation information for this dataset can be found in Data.gov's References section.