This survey was carried out with the objective of providing information on the range of seabed sediment biology throughout the length of the waterway. A total of forty sample stations, located from the lower reaches of both eastern and western Cleddau through the waterway to the entrance of Milford Haven off St Ann's Head, were sampled for biology and sediment composition. A 'reference' station was sampled adjacent to the offshore Island of Skomer for Comparative purposes. Quantitative biological samples were obtained from thirty six stations, by 0.1m2 day grab. Qualitative samples were obtained from two stations and two were found to be unsuitable for grab sampling. Sediment samples were obtained at each location for faunal and sedimentological analyses and samples collected for other analyses. Processing of the biological samples was carried out separately on both 1.0 mm and 0.5 mm sieve mesh size fractions, and this information has been pooled for the purpose of habitat records entered on the MNCR database. Biological sample processing involved identification of more than 125,400 individual animals from 418 quantitative and 38 qualitative taxa. Records currently considered sensitive have been removed from this dataset.