Filter-feeding molluscan shellfish (oysters, mussels, clams, and so forth) are grown in areas classified for sanitary quality under EU Regulation 854/2004 on the basis of Escherichia coli monitoring. Rationalizing monitoring programs through use of a single-indicator shellfish species, rather than monitoring several species, has the benefit of reducing cost. To protect public health, the indicator must show an equivalent or higher level of contamination than the species it represents. This study, using a well-established statistical method (Bland-Altman method comparison) on routine monitoring data, demonstrates that the contamination ratio between species at the same site may change across the range of contamination levels. Nevertheless, an accumulation ordering was established as follows: The common cockle Cerastoderma edule, Tapes philippinarum (Manila clam), and Mytilus spp. (mussels) are broadly equivalent, and each shows a greater level of accumulation than the oysters Crassostrea gigas (Pacific oyster) and Ostrea edulis (native oyster), which both accumulate to a similar extent. Last, Ostrea edulis shows a greater level of accumulation than Mercenaria mercenaria (American hard clam). The data suggest that the use of Mytilus spp. may alone provide an adequate index of fecal pollution impacting the growing areas in England and Wales.