These data were collected to evaluate the cover and composition of native and nonnative vascular plant species within the riparian zone of the Colorado River from Glen Canyon Dam to the historic high-water line of Lake Mead, approximately 240 river miles downstream of Lees Ferry. The overall objective of the ongoing study these data were collected for is to determine how plant cover and composition change over time in response to the operation of Glen Canyon Dam. This includes evaluating how plants respond to climate and other environmental factors, so that the effects of Glen Canyon Dam can be determined. These data represent 36 of the most common plant species observed in sample frames, estimates of how much aerial cover those plants have, and estimates of environmental variables associated with the sample frames. These data were collected from the riparian zone along the Colorado River between Lees Ferry, AZ and the confluence of the Colorado River and Diamond Creek, AZ. Data were collected in August and September for the years 2016, 2017, 2018, 2019, and 2020. These data were collected by the U.S. Geological Survey Grand Canyon Monitoring and Research Center riparian plant program. These data are a combination of field observations and data downloaded from other sources. These data can be used to understand the general distributions of the 36 plant species in the study area at a given time and their change in cover and composition over time. These data are particularly suited to determine the environmental variables that are most related to the cover and occurrence of these 36 plant species.