The sandbanks feature in Carmarthen Bay and Estuaries SAC consists of a single sandbank, Helwick Bank, located to the south of Worms Head. The Helwick Bank is a linear, shallow, subtidal sandbank that is unusual in being one of the most highly exposed to wave and tidal action of all the Welsh sandbanks. The seabed sediments of the Helwick Bank area are predominantly uniform, medium fine sands with little or no fine or organic material.

The animal communities found in and on Helwick Bank are mostly characteristic of mobile sands and gravels, with the exception of those to the south of the bank. Many species spend most of their time wholly or partly buried in the sediment. Communities are dominated by polychaetes. The sandbanks show an increasing species richness in deeper water where the sediments are more stable. Fish, such as turbot, lemon sole and whiting and burrowing species e.g. sand eels, use the Helwick Bank for spawning and as nursery and feeding grounds. Harbour porpoise is evident all along the Helwick Channel from Worms Head eastwards. Pods of short-beaked common dolphin are summer visitors, between Worms Head and the Helwick Bank together with large rafts of Manx shearwater and diving gannets.