This study was the first to be undertaken since 1901, since when natural and industrial changes had occurred to affect the habitat. Observations are reported here for the banks of the north and south shores, using certain points as reference. Features of the 2 shores are described, and an inventory given of the fauna of the banks. Hydrozoan Cnidaria, Bryozoans, Annelids, Molluscs, Crustacea and fish are listed with notes, and particular attention is given to the crabs found (Rhithropanopeus harrisii tridentatus). The monthly distribution of crab sizes and sexes is given, and the species of animals found in association with crabs is shown to vary according to the site studied. The percentage of female crabs found to be fertile each month was investigated, and the relationship between fertility and size is tabulated. Information is summarized in a diagram of the distribution of principal animal species in the estuary. The 3 regions in to which the estuary can now be divided differ from those recognized in 1901, and will in their turn be transitory.