This study concerns the seasonal variation of bacteria in seawater and mussels harvested from a Moroccan coastal area subject to clandestine shellfishing. The changes in the level of bacterial counts of mussels from harvest to sale are also presented. Both seawater and mussels showed regular increases in bacterial loads from fall to summer. Freshly harvested mussels and market mussels were the most contaminated, while freshly shucked mussels, obtained by removing shells after heating shellstock, were the least contaminated. Heating, traditionally used to remove shells, was found to reduce the initial bacterial loads by 72%. However, the storage of shucked mussels for 6 to 8 h at ambient temperatures prior to marketing resulted in an increase in the number of bacteria either due to recontamination or by growth of survivors. Thus, market mussels were 20 to 86 times more contaminated than shellstock and shucked mussels, respectively. No human pathogens were found, but several species of marine vibrios were identified.