This data release contains phytoplankton data and vertical profile measurements of water quality and light in oligotrophic (low nutrient) lakes within the Adirondack Park, New York State. Data were collected between June and October 2021 at five lakes. Four lake locations (Nearshore, Open Water, Layer, Bloom) were sampled representing one of four sample types (Bottom Sediment, Surface Water, Bloom Material, Layer). Water-quality field parameters (water temperature, dissolved-oxygen concentration and percent saturation, pH, specific conductance, turbidity, chlorophyll fluorescence, phycocyanin fluorescence, and fluorescent dissolved organic material) were measured at each sampling location from the surface to the bottom of the water column. Photosynthetically Active Radiation (PAR) was measured at each Open Water site from the surface to the depth where PAR was less than 1 percent of the surface measurement. Bloom and Layer sample types were collected on an opportunistic basis, as observed. PhycoTech, Inc. identified and enumerated the phytoplankton in water and bottom sediments. Phytoplankton were identified to the lowest possible taxonomic level with abundance (reported as both natural units and cells) and biovolume reported.