These data were compiled to fit Bayesian state-space growth in length models to estimate the environmental variables that influence flannelmouth sucker growth rates in the Grand Canyon. Objective(s) of our study were to quantify monthly intervals of growth of flannelmouth suckers in four river reaches, and test if novel high frequency gross primary productivity data would be a significant predictor of fish growth. These data represent capture histories for flannelmouth sucker (Catostomus latippinis) in the mainstem of the Colorado River within the Grand Canyon (river mile 0 to 226) from 2012-2018 and environmental variable data including water temperature, turbidity, and gross primary productivity. Fish data refer to fish length (>150mm fork length), month of capture and spatial location for captures of flannelmouth sucker. These data were collected in the segment of the Colorado River that is within the Grand Canyon, Arizona, between April 2012 to October 2018. Mean monthly water temperature and turbidity data were collected at USGS stream gages at four locations on the Colorado River, and mean monthly gross primary productivity data was collected daily via four Yellow Springs Instrument (YSI) sonds at the same four locations as the stream gages. These data were collected by US Geological Survey, US Fish & Wildlife Service, National Parks Service and Arizona Department of Game and Fish, with funding from the Bureau of Reclamation. Fish data were collected using boat electrofishing and hoop nets, and environmental data was obtained from USGS stream gages. These data can be used to look at spatial and temporal variations in flannelmouth sucker growth.