Submerged aquatic vegetation (SAV) is an important habitat and site of primary production in many aquatic ecosystems but there was no baseline information on SAV extent or distribution in the tidal freshwater Hudson River. In 1994, a collaboration was initiated between the Institute of Ecosystem Studies (IES), the Hudson River National Estuarine Research Reserve/NYSDEC, the Cornell Laboratory for Environmental Applications of Remote Sensing (CLEARS), now the Cornell Institute for Resource Information Systems (IRIS) <http://www.css.cornell.edu/iris/>. In addtion, the New York Sea Grant, the Hudson River Estuary Program, and the National Oceanic and Atmospheric Administration (NOAA) are identified as partners. These groups provided diverse expertise to enable the first broad delimitation of SAV in the Hudson. The project was undertaken in two separate time periods with different sources of funding. In 1995, Phase I (Hyde Park to Castleton) was initiated with National Oceanic and Atmospheric Association and Hudson River Foundation funds. Subsequently in 1997, the remaining portions (Hastings to Hyde Park and Castleton to Troy) were undertaken in Phase II with New York. State Environmental Protection Funds through the Hudson River Estuary Program.