The Ribble, Duddon and Ravenglass estuary systems drain into the eastern basin of the Irish Sea. These estuaries have general west to east orientation which gives rise to a marked gradient of decreasing wave exposure with increasing distance east. In contrast, there is a salinity gradient of low salinity at the tidal limit in the east to near full salinity at the entrance of the estuary in the west. The Ribble Estuary has been extensively modified by man and receives a considerable anthropogenic input of waste material. In contrast, the Duddon and Ravenglass estuary systems are set in rural areas with little anthropogenic influence. Habitats within these estuaries are predominantly sedimentary with occassional small areas of small stones and shingle on the surface of the sediment. Hard substrata is restricted to man-made structures such as coast protection, training walls and railway bridges. Consequently, habitat diversity was low with only ten community types identified within the three estuarine systems. Communities on hard substrata had a low species richness and low abundance which was probably a consequence of low salinity, siltation and/or tidal scour. Sedimentary communities were characterised by infaunal species with few epibenthic species recorded. At the entrance to these estuaries, mobile medium and fine sand flats had a low species richness with occasional polychaetes and crustaceans. In the middle estuaries, sediment became muddier and species richness initially increased with infaunal communities characterised by polychaetes, burrowing crustaceans and bivalve molluscs. With increasing distance up the estuary towards the tidal limit, sediment changed to mud and the ambient salinity declined. Species richness of the infaunal community decreased, the communities were characterised by oligochaete worms and burrowing crustaceans. At the tidal limit, marine species richness declined to zero and freshwater species were recorded. Beware! the infauna has been entered in the epifauna window