Estuaries are coastal inlets where there is generally a large freshwater influence.

Regular visitors to these areas include nationally important numbers of wildfowl which pass through on their winter migration, stopping for a vital ‘refuelling’. Intertidal mudflats draining into the main waterway support rich and productive shellfish and worm communities. 

The estuaries feature in the Carmarthen Bay and Estuaries SAC comprises the Three Rivers estuary complex (Tywi, Taf and Gwendraeth) and Loughor estuary, commonly called the Three Rivers and Burry Inlet estuaries.

The estuaries in Carmarthen Bay And Estuaries SAC contain both subtidal and intertidal habitats, although the latter are a lot more extensive in this SAC.