The timing of life-history events in many plants and animals depend on specific environmental conditions that fluctuate with seasonal conditions. Climate change is altering environmental regimes and disrupting natural cycles and patterns across communities. Anadromous fishes that migrate between marine and freshwater habitats to spawn are particularly sensitive to shifting environmental conditions, and thus are vulnerable to the effects of climate change. However, for many anadromous fish species the specific environmental mechanisms driving migration and spawning patterns are not well understood. The data in this release are a supplement to the publication Legett et al. (2021). Daily patterns of river herring (Alosa spp.) spawning migrations: environmental drivers and variation among coastal streams in Massachusetts. Trans. Am. Fish. The aim of the study was to investigate the upstream spawning migrations of river herring (Alosa spp.) in 12 coastal Massachusetts streams.The results are pairwise comparisons for seasonal river herring run dynamics and environmental regimes among the streams.