 How can we quantify the health of our freshwater streams, rivers and lakes as they respond to changes in climate, land use and biological invasions? Hydrologic variables such as stream flow, seasonal transitions and water quality are important drivers and indicators of aquatic ecosystem function. A change in community composition can be a bellwether for changes in the health of the ecosystem as a whole. To better understand these processes, scientists from the National Ecological Observatory Network, or NEON, are collecting data to understand changes in climate, hydrology, biogeochemical processes, organism populations, habitat structure and much more at field sites across the United States as part of an ambitious program designed to provide researchers with unprecedented amounts of ecological data. When possible, aquatic field sites are co-located with NEON's terrestrial field sites to enable the complementary study of the complete ecosystem. NEON collects data from streams, rivers and lakes using three standardized and interrelated data collection systems, observational field sampling, automated instruments and airborne remote sensing. All three are standardized across field sites while automated and remote sensing instruments are routinely calibrated. This enables direct comparison among sites in between types of data over NEON's lifetime, contributing to a more accurate and detailed picture of ecosystem function and change on a local, regional and continental scale. To better understand the design of freshwater aquatic sites, let's take a closer look at each type. NEON stream sites are reaches of flowing water up to one kilometer long that are free of major flow obstructions or major tributaries. The length of the reach allows for data to be collected across multiple habitat types like pools, riffles and runs. NEON's river sites are stretches of flowing water that are navigable by boat. Similar to streams, NEON river sites were chosen to allow year-round access to a one kilometer reach for field measurements and sampling. The river reach includes shoreline characteristics representative of the region and includes the placement of a buoy in a location that captures the main flow. NEON lakes are lentic bodies of water that may or may not stratify during the year. The lake sites have surface area, depth, hydrologic flow and shoreline characteristics that are representative of the region where they are located. Each lake also has a buoy in the deepest basin. At each site, NEON field scientists collect regular observations of aquatic microbes, algae, plants, macroinvertebrates, zooplankton and fish. Over time, these data provide a better understanding of how organismal populations and communities change within aquatic ecosystems. Genomic data are collected from macroinvertebrates, aquatic microbes, zooplankton and fish. Biogeochemical measurements are collected from surface water, groundwater, sediments, aquatic plants and microalgae. Regular riparian vegetation assessments provide data on the surrounding vegetation structure. A subset of biological samples are archived in the NEON biorepository and are available upon request. Field scientists create pathometry and morphology maps of each aquatic site allowing comparison of physical properties over time. Instruments are installed at each aquatic field site to collect measurements of the surface water, groundwater and meteorological conditions. Up to eight shallow groundwater wells are installed at each site to collect data about groundwater elevation, temperature and specific conductance. A meteorological station is located in the riparian area and configured with a subset of the sensors that are deployed on NEON's terrestrial flux towers. A phenocam is installed nearby, facing the water to capture time-lapse imagery of how the vegetation and water surface change throughout the year. At river and lake sites, a second meteorological station is placed on the buoy over the water to collect above-water meteorological conditions. The buoy is also outfitted with sensors that collect chemical and physical data at multiple depths in the water. At river sites, another aquatic sensor station is positioned near the shore to collect surface water elevation and other data. At lakes, two equivalent sensor stations are located near shore in the littoral zone. At stream sites, a pair of aquatic sensor stations are located in the main flow, with the upstream to downstream distance dictated by average flow conditions. NEON conducts airborne remote sensing surveys of all field sites. Using discrete and waveform lidar, spectrometry data and high-resolution digital camera images, NEON's airborne observation platform matched the land surface of each field site, providing information about vegetation and landform composition, chemistry and structure. NEON's standardized methods and collection systems allow for users to compare data within a single field site and across multiple field sites to answer more complex ecosystem questions. For example, using NEON data, scientists can study the changing characteristics and composition of aquatic micro-populations at a field site in relation to surface water data and remote sensing-derived ecosystem structure maps. Researchers can then apply these data to how aquatic micro-populations are impacted by environmental conditions at different sites. This will result in improving the ability to detect and predict the changing health of our aquatic ecosystems. So, from the sky down into streams, rivers, lakes and groundwater, NEON is collecting a wide variety of ecological data at different spatial and temporal scales. Automated measurements happen every second of the day at the meteorological and aquatic sensor stations, weekly field sampling covers a broader area, and NEON's annual remote sensing surveys collect watershed scale data. Visit neonscience.org to learn more.