estuary
as defined in Council Directive 91/271/EEC of 21 May 1991 concerning urban waste-water…, Article 2, point (12)
the transitional area at the mouth of a river between fresh-water and coastal waters. Member States shall establish the outer (seaward) limits of estuaries for the purposes of this Directive as part of the programme for implementation in accordance with the provisions of Article 17 (1) and (2)