Benthic survey of Glaswyn/Dwyryd Estuary sandflats, adjacent to Morfa Harlech NNR. The estuary is extensive at 8.2 km. Sediments are of marine sand collected by Langshore drift in Coreligan Bay, and accretion in the estuarine area. Two obvious faunal trends ar apparent when the main part of the estuary. A salinity trend restricting Anguilla tenuis and Bathyporeia pelagica to low ground near the mouth and a sand/mobility/shelter/height based trend from the sparse fauna of the sandy low water channels to the organically richer muddy salt marsh fringe. The basin just above Portmadoc town bridge is an especially muddy artificial habitat sheltered by embankments and adjacent to the town sewage works. This mud seems to hold Nereis diversicolor, Prionospio cirifera and oligochaetes.