This dataset presents observations and measurements of riparian plant invasion, community composition, and environmental conditions at 238 bridge crossings in four western USA river basins: the Colorado Headwaters, upper/middle Rio Grande, upper Arkansas River, and South Platte River (281,946 square kilometers). The 238 sites are a stratified random sample of all bridge crossings in the river basins, with roughly equal numbers of sites in landscapes dominated by (1) urban and residential (developed) land-use, (2) agricultural (cultivated) land-use, and (3) undeveloped land cover. The dataset includes field observations of stem counts for three non-native riparian woody plant taxa (Tamarix ramosissima x T. chinensis hybrids - tamarisk or saltcedar, Elaeagnus angustifolia - Russian olive, Ulmus pumila - Siberian elm) in each of four size classes for each taxon, to evaluate presence, stem density, and size class distributions of these taxa. Second, it includes field observations ranking the five woody taxa with the highest cover in the riparian floodplain, to evaluate overall riparian plant community composition as well as rank dominance of the three non-native taxa. Third, the dataset includes various measures of environmental conditions at the sites, including adjacent human land-use, nearby human planting of the three non-native taxa, mean annual temperature and precipitation, watershed drainage area, streamflow intermittency, upstream reservoir storage, streambank stabilization, floodplain domestic grazing, and riparian forest cover. Some environmental conditions were measured in the field, some were measured in aerial photographs, and some measurements were obtained from previously existing data layers. Fourth, the dataset includes presence/absence data for the three non-native taxa across a wider area of the floodplain at a subset of the sites that had been sampled previously in 1997-2001 for a separate dataset (n=33 including two that were not included in the 238 sites described above).