The U.S. Geological Survey (USGS) has been collecting streamflow information for the Nation's streams since 1889. The USGS has been involved in developing and using acoustic flow measurement technology since the late 1960s to improve the accuracy of an efficiency of streamflow measurements. Since the early 1980s the USGS has worked cooperatively with manufactures to develop and enhance the use of acoustic Doppler instruments. ADCP performance and operational characteristics are changing frequently as hardware and software continue to improve. Frequent revisions of software, firmware, and documentation revisions are expected in the foreseeable future. The purpose of this website, supported by the Office of Surface Water, is to provide relevant information to hydroacoustic technology users in the USGS; however, most of the information provided herein is available to all users of hydroacoustic technology.