This dataset records Cladophora and associated submerged aquatic vegetation (SAV) biomass collected approximately monthly during the growing season of 2019 at stations located along the U.S. shoreline of Lakes Michigan, Huron, Erie, and Ontario. It also records a variety of supporting data collected at Cladophora measurement stations. These supporting data include: - seasonal time series of light, currents, wave action, temperature, specific conductivity, turbidity, pH, phycocyanin, chlorophyll, and dissolved oxygen from moored sensors at a subset of stations; - measurements of Secchi disk depth and water chemistry; - water column profiles of temperature, specific conductivity, turbidity, pH, phycocyanin, chlorophyll, and dissolved oxygen; - diver observations of SAV, dreissenid mussels, round goby abundance, and substrate properties; - measurements of dreissenid mussel abundance and size class distribution coincident with SAV biomass; - nutrient content of SAV, dreissenid mussels, and sediments; - and information about sampling locations and operations. Similar data were collected in 2018 at seven of the same transects within four Great Lakes and is available at https://doi.org/10.5066/P9E570JS. This is a revised version of data release; all changes are described in the ReleaseHistory_Cladophora2019_v2.txt. First posted: September 25, 2020 Revised: December, 2023