composed primarily of fresh water estuarine open water surface layer estuarine tidal riverine open water surface layer This class aligns to the Coastal and Marine Ecological Classification Standard (CMECS). In ENVO, we may adapt the definition for consistency, but the semantics (meaning) of the term should be unaffected. Please consult the CMECS catalogue (https://cmecscatalog.org/) for authoritative and semantically unconstrained definitions. What causes this freshwater layer to be "tidal" is not clearly specified in the current CMECS definition. envoCmecs CMECS:607 envoMarine A layer of fresh, tidal estuarine water which extends a few centimeters from the surface of the water column towards the estuary bed and from a fiat boundary where the estuary bed below the water column reaches a depth of 4 meters until the end of the estuary most distal from the coast. https://cmecscatalog.org/cmecs/classification/unit/607.html