ETI estuary types: SIDE (shallow intertidal dominated estuaries), SSRTRE (shallow, short residence time estuaries), DSDE (deeper subtidal dominated, longer residence time estuaries) and coastal lakes (freshwater-dominated). SIDE and SSRTRE types (broadly, ‘lagoon’ or ‘river’ estuaries, respectively) also have the subtype ICOE, to indicate if they are intermittently closed or open estuaries, rather than always open, to the sea.