Tidal stream A stream reach where the flow is influenced by the tide, but where the water chemistry is not normally influenced. A site where ocean water typically mixes with stream water should be coded as an estuary. 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.