This collection contains slide-mounted subsamples of aquatic microalgae (NEON sample class: ptx_taxonomy_in.slideID). Periphyton and phytoplankton samples are collected three times per year at wadeable stream, river, and lake sites during aquatic biology bout windows, roughly in spring, summer, and fall. Benthic samples are collected using the most appropriate sampler for the habitat and substratum type, including rock scrubs, grab samples, and epiphyton. In wadeable streams, periphyton samples are collected in the two most dominant benthic habitat types (e.g. riffles, runs, pools, step pools), and seston samples were collected from the water column near the S2 sensor (seston samples were discontinued in 2018). In lakes, water-column phytoplankton samples are collected near the buoy and littoral sensors using a Kemmerer sampler, and in littoral areas using the best benthic sampling method for the dominant substratum type. In rivers, phytoplankton samples are collected near the buoy and two other deep-water locations using a Kemmerer or Van Dorn sampler, and in littoral areas using the best benthic sampling method for the dominant substratum type. All field-collected samples are split into subsamples in the domain support facility, preserved, and shipped to a contracting taxonomy laboratory where samples are further subsampled for analysis and archiving. Algae specimens in this collection contain cleaned diatom subsamples that have been mounted on glass microscope slides and are archived at room temperature. See related links below for protocols and NEON related data products.