This dataset shows the temporal frequency and spatial extent of cyanobacteria cells in large, freshwater lakes and reservoirs across the continental United States derived from 300x300 meter MEdium Resolution Imaging Spectrometer (MERIS) satellite imagery from 2002-2012 and functionally similar Ocean and Land Colour Instrument (OLCI) satellite imagery from 2017-2021. This dataset was produced through a partnership with the National Oceanic and Atmospheric Administration (NOAA), the National Aeronautics and Space Administration (NASA), the United States Geological Survey (USGS), and the United States Environmental Protection Agency (USEPA). This cyanobacteria dataset was derived using the European Space Agency's (ESA) Envisat MERIS sensor and their Sentinel-3 OLCI sensor. MERIS and OLCI are nadir-pointing imaging spectrometers which measure the solar radiation reflected by the Earth in 15 and 21 spectral bands, respectively (visible through near-infrared). MERIS and OLCI imagery was used to identify long-wavelength spectral bands (from red through near-infrared portion of the spectrum) to locate algal blooms within freshwaters and estuaries of the continental United States. EnviroAtlas allows users to spatially explore this cyanobacteria data in the online interactive map viewer. EnviroAtlas (https://www.epa.gov/enviroatlas) allows the user to interact with a web-based, easy-to-use, mapping application to view and analyze multiple ecosystem services for the continental United States. The dataset is available as downloadable data (https://oceancolor.gsfc.nasa.gov/CYAN/) or as an EnviroAtlas map service. Additional descriptive information about each attribute in this dataset can be found in its associated EnviroAtlas Fact Sheet (https://www.epa.gov/enviroatlas/enviroatlas-fact-sheets).