The depth at which these incredible bivalves feed has earned them the reputation and connotation of being a bottom-feeder which is incorrect. Both black and green mussels are filter feeders, which means that they filter plankton, their food, from the surrounding water. The mussel sucks in nutrient-filled water and excretes wastewater which is where the risk arises. While it is true that harmful algal blooms and other toxins can contaminate mussels, the vast majority of commercially produced filter-feeding shellfish are safe to eat. In the US, the FDA uses The National Shellfish Sanitation Program (NSSP) and other endeavors to ensure that mussels and other shellfish are safe for consumption.