A global, encompassing characterisation of an estuary is “a semi-enclosed coastal body of water which has a free connection with the open sea and within which sea water is measurably diluted with fresh water derived from land drainage”1. This does not fully address every South African estuary, in that the majority are small, have limited access to the sea, close for long-periods and back-flood into supporting habitats, and when open are influenced by only micro-tidal regimes.
A better definition for the South African context is “a partially enclosed coastal body of water which is either permanently or periodically open to the sea and within which there is measurable variation of salinity due to the mixture of seawater with fresh water derived from land drainage”2. The classification of an estuary as laid out in the ICM Act (24 of 2008, amended by Act 36 of 2014) very closely follows this; “a body of surface water that is permanently or periodically open to the sea, in which a rise and fall of the water level as a result of the tides is measurable at spring tides when the water course is open to the sea, or in respect of which the salinity is higher than freshwater as a result of the influence of the sea, and where there is a salinity gradient between the tidal reach and the mouth of the body of surface water”.
