Estuary A coastal inlet of the sea or ocean; esp. the mouth of a river, where tide water normally mixes with stream water (modified, Webster). Salinity in estuaries typically ranges from 1 to 25 Practical Salinity Units (psu), as compared oceanic values around 35-psu. See also: tidal stream and coastal. Surface Water Sites Adapted from USGS Site Types. http://wdr.water.usgs.gov/nwisgmap/help/sitetype.html ODM2 SiteType Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of a data collection Site. To some extent, these types represent the ultimate feature of interest that the site was established to measure. For example, a Stream Site was established to measure properties of a Stream.